Codebook Subset Restriction for Full-Dimension MIMO

ABSTRACT

A method, in a radio network node, comprises identifying, among a predetermined codebook of precoding matrix codewords, a subset of precoding matrix codewords that are not to be reported by the wireless device ( 90 ) in channel-state-information, CSI, feedback, and transmitting, to the wireless device ( 90 ), a bitmap identifying the subset of precoding matrix codewords that are not to be reported by the wireless device ( 90 ); where each bit in the bitmap corresponds to only one combination of a first dimension index l′ 1  and a second dimension index l′ 2  out of the possible combinations of the first dimension index l′ 1  and the second dimension index l′ 2 , and where the first dimension index l′ 1  and the second dimension index l′ 2  identify a two-dimensional beam, the two-dimensional beam being defined by a vector of complex numbers comprised within at least one column of a precoding matrix codeword in the codebook.

TECHNICAL FIELD

Embodiments herein relate to wireless communications in general and inparticular to methods and apparatuses for managing precoder codewordselection in wireless systems supporting full-dimension multiple-inputmultiple-output (FD-MIMO) transmission schemes.

BACKGROUND

The 3rd Generation Partnership Project (3GPP) is responsible for thestandardization of the Universal Mobile Telecommunication System (UMTS)and Long Term Evolution (LTE). The 3GPP work on LTE is also referred toas Evolved Universal Terrestrial Access Network (E-UTRAN). LTE is atechnology for realizing high-speed packet-based communication that canreach high data rates both in the downlink and in the uplink, and isthought of as a next generation mobile communication system relative toUMTS. In order to support high data rates, LTE allows for a systembandwidth of 20 MHz, or up to 100 MHz when carrier aggregation isemployed. LTE is also able to operate in different frequency bands andcan operate in at least Frequency Division Duplex (FDD) and TimeDivision Duplex (TDD) modes.

LTE uses Orthogonal Frequency-Division Multiplexing (OFDM) in thedownlink and Discrete-Fourier-Transform-spread (DFT-spread) OFDM in theuplink. The basic LTE downlink physical resource can thus be seen as atime-frequency grid as illustrated in FIG. 1, where each resourceelement corresponds to one OFDM subcarrier during one OFDM symbolinterval.

In the time domain, LTE downlink transmissions are organized into radioframes of 10 milliseconds, as shown in FIG. 2, with each radio frameconsisting of ten equally-sized subframes of length Tsubframe=1millisecond. For normal cyclic prefix, one subframe consists of fourteenOFDM symbols. The duration of each OFDM symbol is approximately 71.4microseconds (μs).

Furthermore, the resource allocation in LTE is typically described interms of resource blocks, where a resource block corresponds to one slot(0.5 ms) in the time domain and twelve contiguous subcarriers in thefrequency domain. A pair of two adjacent resource blocks in timedirection (1.0 ms) is known as a resource block pair. Resource blocksare numbered in the frequency domain, starting with 0 from one end ofthe system bandwidth.

Downlink transmissions are dynamically scheduled, i.e., in each subframethe base station transmits control information about to which terminalsdata is transmitted and within which resource blocks the data istransmitted, in the current downlink subframe. This control signaling(PDCCH) is typically transmitted in the first one, two, three, or fourOFDM symbols in each subframe and the number n=1, 2, 3 or 4 is known asthe Control Format Indicator (CFI). The downlink subframe also containscommon reference symbols, which are known to the receiver and used forcoherent demodulation of the control information, for example. A portionof a downlink subframe with CFI=3 OFDM symbols as control is illustratedin FIG. 3.

From Release 11 of the 3GPP specifications for LTE (LTE Rel-11) onwards,the above described resource assignments can be scheduled on theEnhanced Physical Downlink Control Channel (EPDCCH) as well as on thePhysical Downlink Control Channel (PDCCH). For Rel-8 LTE to Rel-10 LTE,only the PDCCH is used for this purpose.

The reference symbols shown in FIG. 3 are the cell-specific referencesymbols (CRS) and are used to support multiple functions including finetime and frequency synchronization and channel estimation for certaintransmission modes.

In a cellular communication system there is a need to measure thechannel conditions, in order to know what transmission parameters touse. These parameters include, e.g., modulation type, coding rate,transmission rank, and frequency allocation. This applies to uplink (UL)as well as downlink (DL) transmissions.

The scheduler that makes the decisions on the transmission parameters istypically located in the base station (referred to in 3GPP documentationas an “eNB”). Hence, it can measure channel properties of the ULdirectly using known reference signals that the terminals (referred toin 3GPP documentation as “user equipment” or “UEs”) transmit. Thesemeasurements then form a basis for the UL scheduling decisions that theeNB makes, which are then sent to the UEs via a downlink controlchannel.

Multi-antenna techniques can significantly increase the data rates andreliability of a wireless communication system. The performance isparticularly improved if both the transmitter and the receiver areequipped with multiple antennas, which results in a multiple-inputmultiple-output (MIMO) communication channel. Such systems and/orrelated techniques are commonly referred to as MIMO.

The LTE standard is currently evolving to include enhanced MIMO support.A core component in LTE is the support of MIMO antenna deployments andMIMO related techniques. Currently, LTE-Advanced supports an 8-layerspatial multiplexing mode for eight transmit (Tx) antennas, with channeldependent precoding. The spatial multiplexing mode is aimed for highdata rates in favorable channel conditions. An illustration of thetransmission structure for precoded spatial-multiplexing operation isprovided in FIG. 4.

As seen in FIG. 4, the information carrying symbol vectors is multipliedby an N_(T)×r precoder matrix W, which serves to distribute the transmitenergy in a subspace of the N_(T)-dimensional vector space, where N_(T)is the number of transmitting antenna ports. The precoder matrix istypically selected from a codebook of possible precoder matrices, andtypically indicated by means of a precoder matrix indicator (PMI), whichspecifies a unique precoder matrix in the codebook for a given number ofsymbol streams. The r symbols in s each correspond to a layer, and r isreferred to as the transmission rank. In this way, spatial multiplexingis achieved, since multiple symbols can be transmitted simultaneouslyover the same time/frequency resource element (TFRE). The number ofsymbols r is typically adapted to suit the current channel properties.

As noted above, LTE uses OFDM in the downlink (and DFT-precoded OFDM inthe uplink), and hence the received N_(R)×1 vector y_(n) for a certainTFRE on subcarrier n (or alternatively data TFRE number n) is modeledby:

y _(n) =H _(n) Ws _(n) +e _(n),

where N_(R) is the number of receiver antenna ports and e_(n) is anoise/interference vector obtained as realizations of a random process.The precoder W can be a wideband precoder, which is constant overfrequency, or frequency selective.

The precoder matrix is often chosen to match the characteristics of theN_(R)×N_(T) MIMO channel matrix H_(n), resulting in so-calledchannel-dependent precoding. This is also commonly referred to asclosed-loop precoding, and essentially strives to focus the transmitenergy into a subspace that is strong, in the sense of conveying much ofthe transmitted energy to the UE. In addition, the precoder matrix mayalso be selected to strive for orthogonalizing the channel, meaning thatafter proper linear equalization at the UE, the inter-layer interferenceis reduced.

The transmission rank, and thus the number of spatially multiplexedlayers, is reflected in the number of columns of the precoder. Forefficient performance, it is important that a transmission rank thatmatches the channel properties is selected.

In LTE Release-10, a new reference symbol sequence or reference signal,referred to as CSI-RS, was introduced for purposes of estimating channelstate information (CSI). The CSI-RS provides several advantages overbasing CSI feedback on the common or cell-specific reference symbols(CRS) which were used for that purpose in previous releases. Firstly,the CSI-RS is not used for demodulation of the data signal, and thusdoes not require the same density, i.e., the overhead of the CSI-RS issubstantially less than that of the CRS. Secondly, CSI-RS provides amuch more flexible means to configure CSI feedback measurements (e.g.,which CSI-RS resource to measure on can be configured in a UE specificmanner).

By measuring on a CSI-RS, a UE can estimate the effective channel theCSI-RS is traversing, where the effective channel includes the radiopropagation channel and antenna gains. In more mathematical rigor thisimplies that if a known CSI-RS signal x is transmitted, a UE canestimate the coupling between the transmitted signal and the receivedsignal, i.e., the effective channel. Hence, if no virtualization isperformed in the transmission, the received signal y can be expressedas:

y=Hx+e

and the UE can estimate the effective channel H.

Up to eight CSI-RS ports can be configured for a Rel-11 UE, which meansthat the UE can thus estimate the channel from up to eight transmitantennas.

For CSI feedback, LTE has adopted an implicit CSI mechanism where a UEdoes not explicitly report, e.g., the complex-valued elements of ameasured effective channel, but rather the UE recommends a transmissionconfiguration for the measured effective channel. The recommendedtransmission configuration thus implicitly gives information about theunderlying channel state.

In LTE, CSI feedback is given in terms of a transmission rank indicator(RI), a precoder matrix indicator (PMI), and one or two channel qualityindicator(s) (CQI). The CQI/RI/PMI report can be wideband or frequencyselective, depending on which reporting mode is configured.

The RI corresponds to a recommended number of streams that are to bespatially multiplexed and thus transmitted in parallel over theeffective channel. The PMI identifies a recommended precoding matrixcodeword (in a codebook which contains precoders with the same number ofrows as the number of CSI-RS ports) for the transmission, which relatesto the spatial characteristics of the effective channel. The CQIrepresents a recommended transport block size, i.e., code rate, and LTEsupports transmission of one or two simultaneous transmissions oftransport blocks on each of up to four different layers, i.e.,separately encoded blocks of information, to a UE in a subframe. Thereis thus a relation between a CQI and an SINR of the spatial stream(s)over which the transport block or blocks are transmitted.

Recent development in 3GPP has led to the discussion of two-dimensionalantenna arrays where each antenna element has an independent phase andamplitude control, thereby enabling beamforming in both in the verticaland the horizontal dimensions. Such antenna arrays may be (partly)described by the number of antenna columns corresponding to thehorizontal dimension N_(h), the number of antenna rows corresponding tothe vertical dimension N_(v), and the number of dimensions correspondingto different polarizations N_(p). The total number of antennas is thusN=N_(h)N_(v)N_(p). An example of an antenna array where N_(h)=4 andN_(v)=8 is illustrated in FIG. 5. This array furthermore consists ofcross-polarized antenna elements, meaning that N_(p)=2. We will denotesuch an antenna as an 8×4 antenna array with cross-polarized antennaelements. Note that the right-hand side of FIG. 5 shows an exampleantenna port layout corresponding to the same antenna array, with 2vertical ports and 4 horizontal ports. This could be obtained, forinstance, by virtualizing each port with 4 vertical antenna elements,i.e., mapping outputs from 4 vertical antenna elements to each of theports shown on the right-hand side of FIG. 5. Hence, assumingcross-polarized ports are present, the UE can measure CSI-RS for 16antenna ports, in this example.

Precoding may be interpreted as multiplying the signal with differentbeamforming weights for each antenna port prior to transmission. Atypical approach is to tailor the precoder to the antenna form factor,i.e., taking into account N₁, N₂ and N_(p) when designing the precodercodebook.

A common approach when designing precoder codebooks tailored fortwo-dimensional antenna arrays is to combine precoders tailored for ahorizontal array and a vertical array of antenna ports, respectively, bymeans of a Kronecker product. A precoding matrix W in the codebook isthen represented as:

W=W ₁ W ₂,  (Eq. 1)

where W₁ is defined as:

$\begin{matrix}{{W_{1} = \begin{pmatrix}{X_{1} \otimes X_{2}} & 0 \\0 & {X_{1} \otimes X_{2}}\end{pmatrix}},} & \left( {{Eq}.\mspace{14mu} 2} \right)\end{matrix}$

wherein:

-   -   X₁ is a N₁×L₁ matrix (corresponding to a beam group) with L₁        column vectors which are constructed using O₁ times oversampled        Discrete-Fourier-Transform (DFT) vectors v_(l) of length

${{N_{1}\text{:}\mspace{14mu} v_{l}} = \begin{bmatrix}1 & e^{\frac{j\; 2\pi \; l}{N_{1}O_{1}}} & \ldots & e^{\frac{j\; 2{\pi {({N_{1} - 1})}}l}{N_{1}O_{1}}}\end{bmatrix}^{T}};$

-   -   X₂ is a N₂×L₂ matrix (corresponding to a beam group) with L₂        column vectors which are constructed using O₂ times oversampled        DFT vectors u_(l) of length

${{N_{2}\text{:}\mspace{14mu} u_{l}} = \begin{bmatrix}1 & e^{\frac{j\; 2\pi \; l}{N_{2}O_{2}}} & \ldots & e^{\frac{j\; 2{\pi {({N_{2} - 1})}}l}{N_{2}O_{2}}}\end{bmatrix}^{T}};$

-   -   N₁ and N₂ are the numbers of antenna ports per polarization in a        first dimension (e.g., horizontal) and in a second dimension        (e.g., vertical), respectively;    -   L₁ and L₂ are referred to as the beam group sizes of the first        and second dimensions, respectively; and    -   [ ]^(T) denotes the transpose operation.

The matrix W₂ in Eq. 1 selects beams from these beam groups (in the twodimensions). W₂ may operate per subband, to enable fast beam selection(per subband) across the system bandwidth.

In Rel-13 LTE, class A CSI reporting refers to the case where the UEreports CSI using non-precoded CSI reference symbols or signals in boththe first and second dimensions. In Rel-13, parameterized codebooks for12 and 16 ports are supported, in addition to a two-dimensional 8-portcodebook. The Rel-13 class A codebook is configured with five RadioResource Control (RRC) configured parameters:

-   -   The numbers N₁, N₂ of antenna ports per polarization in each        dimension; N₁, N₂ ∈{1, 2, 3, 4, 8}, where the valid candidates        are (N₁, N₂)=(8,1), (2,2), (2,3), (3,2), (2,4), (4,2)    -   The oversampling factors O₁, O₂ in each dimension; For each (N₁,        N₂), configurability of (O₁, O₂) is restricted to two possible        fixed pairs as given below:

(N₁, N₂) (O₁, O₂) combinations (8, 1) (4, —), (8, —) (2, 2) (4, 4), (8,8) (2, 3) {(8, 4), (8, 8)} (3, 2) {(8, 4), (4, 4)} (2, 4) {(8, 4), (8,8)} (4, 2) {(8, 4), (4, 4)}

-   -   A configuration parameter Config that can take on values of 1,        2, 3, or 4.

It should be noted that for the case(s) where one dimension has a singleport, the oversampling factor (for that dimension), and Config values of2 and 3 do not apply.

Rank-1 Class A Codebook

Given the set of values N₁, N₂, O₁, and O₂, the W₁ matrices in Eq. 1 andEq. 2 are constructed with:

$\begin{matrix}{\left( {L_{2}^{\prime},L_{2}^{\prime}} \right) = \left\{ {\begin{matrix}{\left( {4,2} \right),} & {{{if}\mspace{14mu} N_{1}} \geq N_{2}} \\{\left( {2,4} \right),} & {{{else}\mspace{14mu} N_{1}} < N_{2}}\end{matrix},} \right.} & \left( {{Eq}.\mspace{14mu} 3} \right)\end{matrix}$

where L′₁ and L′₂ are the number of columns in X₁ and X₂, respectively.The values of L′₁ and L′₂ are first chosen such that L′₁>L₁ and L′₂>L₂,to form an extended codebook. Depending on the value of Config, a subsetof codewords from the extended codebook is selected as an active subset,i.e. used in CSI feedback, as follows:

Config = 1:  (L₁, L₂) = (1, 1)Config = 2:  (L₁, L₂) = (2, 2)  [square]Config = 3:  (L₁, L₂) = (2, 2)[non-adjacent  two-dimensional  beams/checkerboard]${Config} = {{4\text{:}\mspace{14mu} \left( {L_{1},L_{2}} \right)} = \left\{ \begin{matrix}{\left( {4,1} \right),} & {{{if}\mspace{14mu} N_{1}} \geq N_{2}} \\{\left( {1,4} \right),} & {{{else}\mspace{14mu} N_{1}} < N_{2}}\end{matrix} \right.}$

Hence, config 2-4 contains four beams per beam group while config 1 onlycontains a single beam per beam group. Let i_(1,1)=0, 1, . . . ,O₁N₁/s₁−1 and i_(1,2)=0,1, . . . , O₂N₂/s₂−1 denote the first PMI indexin dimension 1 and 2, respectively. Here, s₁ and s₂ represent beam groupspacing, or how far apart the beam groups can be in angle, in dimension1 and 2, respectively. From the active subset of codewords describedabove, the UE selects one codeword and reports this selection via asecond PMI i′₂ in aperiodic reporting on PUSCH. Hence, the rank-1codebook can be defined in terms of i_(1,1), i_(1,2), and i′₂ as shownin Table 1, below.

TABLE 1 Rank-1 Class A Codebook for N₁ ≥ N₂ i₂′ 0 1 2 3 Precoder W_(s) ₁_(i) _(1,1) _(,s) ₂ _(i) _(1,2) _(,0) ⁽¹⁾ W_(s) ₁ _(i) _(1,1) _(,s) ₂_(i) _(1,2) _(,1) ⁽¹⁾ W_(s) ₁ _(i) _(1,1) _(,s) ₂ _(i) _(1,2) _(,2) ⁽¹⁾W_(s) ₁ _(i) _(1,1) _(,s) ₂ _(i) _(1,2) _(,3) ⁽¹⁾ i₂′ 4 5 6 7 PrecoderW_(s) ₁ _(i) _(1,1) _(+1,s) ₂ _(i) _(1,2) _(,0) ⁽¹⁾ W_(s) ₁ _(i) _(1,1)_(+1,s) ₂ _(i) _(1,2) _(,1) ⁽¹⁾ W_(s) ₁ _(i) _(1,1) _(+1,s) ₂ _(i)_(1,2) _(,2) ⁽¹⁾ W_(s) ₁ _(i) _(1,1) _(+1,s) ₂ _(i) _(1,2) _(,3) ⁽¹⁾ i₂′8 9 10 11 Precoder W_(s) ₁ _(i) _(1,1) _(+2,s) ₂ _(i) _(1,2) _(,0) ⁽¹⁾W_(s) ₁ _(i) _(1,1) _(+2,s) ₂ _(i) _(1,2) _(,1) ⁽¹⁾ W_(s) ₁ _(i) _(1,1)_(+2,s) ₂ _(i) _(1,2) _(,2) ⁽¹⁾ W_(s) _(1,) _(i) _(1,1) _(+2,s) ₂ _(i)_(1,2) _(,3) ⁽¹⁾ i₂′ 12 13 14 15 Precoder W_(s) ₁ _(i) _(1,1) _(+3,s) ₂_(i) _(1,2) _(,0) ⁽¹⁾ W_(s) ₁ _(i) _(1,1) _(+3,s) ₂ _(i) _(1,2) _(,1)⁽¹⁾ W_(s) ₁ _(i) _(1,1) _(+3,s) ₂ _(i) _(1,2) _(,2) ⁽¹⁾ W_(s) ₁ _(i)_(1,1) _(+3,s) ₂ _(i) _(1,2) _(,3) ⁽¹⁾ i₂′ 16-31 Precoder Entries 16-31constructed with replacing the second subscript _(s) ₂ _(i) _(1,2) with_(s) ₂ _(i) _(1,2) ₊ ₁ in entries 0-15.

In Table 1, each rank-1 codeword W_(m) ₁ _(,m) ₂ _(,n) ⁽¹⁾ is defined as

$\begin{matrix}{{W_{m_{1},m_{2},n}^{(1)} = {\frac{1}{\sqrt{Q}}\begin{bmatrix}{v_{m_{1}} \otimes u_{m_{2}}} \\{\phi_{n}{v_{m_{1}} \otimes u_{m_{2}}}}\end{bmatrix}}},} & \left( {{Eq}.\mspace{14mu} 4} \right)\end{matrix}$

wherein φ_(n)=e^(jπn/2). In Eq. 4, the single layer of data istransmitted on the two-dimensional beam involving the m₁ ^(th) beam inthe first dimension and the m₂ ^(th) beam in the second dimension,where:

$\begin{matrix}{v_{m_{1}} = \left\lbrack \begin{matrix}1 & e^{j\frac{2\pi \; m_{1}}{O_{1}N_{1}}} & \ldots & {\left. e^{{j\frac{2\pi \; {m_{1}{({N_{1} - 1})}}l}{O_{1}N_{1}}}\;} \right\rbrack^{T},}\end{matrix} \right.} & \left( {{Eq}.\mspace{14mu} 5} \right) \\{u_{m_{2}} = \left\lbrack {\begin{matrix}1 & e^{j\frac{2\pi \; m_{2}}{O_{2}N_{2}}} & \ldots & {\left. e^{{j\frac{2\pi \; {m_{2}{({N_{2} - 1})}}l}{O_{2}N_{2}}}\;} \right\rbrack^{T},}\end{matrix}.} \right.} & \left( {{Eq}.\mspace{14mu} 6} \right)\end{matrix}$

and where the superscript T indicates matrix transpose.

For each Config value, the different possible values of i′₂ and theassociated values of s₁ and s₂ are given in Table 2.

This codebook can be interpreted as follows: The left column in Table 2describes how the beams in the beam group are distributed across thefirst and second dimension. The indices i_(1,1) and i_(1,2) in Table 1are wideband, and used to select the beams in the beam group. The indexi′₂ is used to perform beam selection within the beam group (as selectedby i_(1,1) and i_(1,2)) and co-phasing of the beams in the differentpolarizations. The parameters s₁ and s₂ indicate the shift betweendifferent beam groups. For instance, Table 1 shows that given i_(1,1),the indices for the first dimension are s₁ i_(1,1), s₁ i_(1,1)+1, s₁i_(1,1)+2, s₁ i_(1,1)+3, while Table 2 shows that for Config 2, only i′₂indices (0-7, 16-23) can be selected, hence only s₁ i_(1,1), +1 can beselected for this configuration. Effectively, the beam group size of thefirst dimension in Config 2 is two, i.e. L₁=2.

Rank-2 Class A Codebook

Given the set of values N₁, N₂, O₁, and O₂, the W₁ matrices in Eqs. 1and 2 are constructed in the same manner described above (i.e., usingthe same values of (L′₁, L′₂) defined in Eq. 3). The rank-2 codebook canbe defined in terms of i_(1,1), i_(1,2), and i′₂ as shown in Table 3below. In Table 3, each rank-2 codeword W_(m) ₁ _(,m) ₂ _(,m) ₁ _(′)_(,m) ₂ _(′) _(,n) ⁽²⁾ is defined as

$\begin{matrix}{{W_{m_{1},m_{2},m_{1}^{\prime},m_{2}^{\prime},n}^{(2)} = {\frac{1}{\sqrt{2\; Q}}\begin{bmatrix}{v_{m_{1}} \otimes u_{m_{2}}} & {v_{m_{1}^{\prime}} \otimes u_{m_{2}^{\prime}}} \\{\phi_{n}{v_{m_{1}} \otimes u_{m_{2}}}} & {{- \phi_{n}}{v_{m_{1}^{\prime}} \otimes u_{m_{2}^{\prime}}}}\end{bmatrix}}},} & \left( {{Eq}.\mspace{14mu} 7} \right)\end{matrix}$

wherein φ_(n)=e^(jπn/2). In Eq. 7, the first layer of data istransmitted on the two-dimensional beam involving the m₁ ^(th) beam inthe first dimension and the m₂ ^(th) beam in the second dimension; thesecond layer of data is transmitted on the two-dimensional beaminvolving the (m₁′)^(th) beam in the first dimension and the (m₂′)^(th)beam in the second dimension. Furthermore, i_(1,1), i_(1,2), and thebeam offsets p₁, and p₂ in Table 3 are defined as:

i _(1,1)=0,1, . . . ,O ₁ N ₁ /s ₁−1

i _(1,2)=0,1, . . . ,O ₂ N ₂ /s ₂−1

p ₁=1 and p ₂=1

TABLE 3 Rank-2 Class A Codebook i₂′ 0 1 Precoder W_(s) ₁ _(i) _(1,1)_(,s) ₂ _(i) _(1,2) _(,s) ₁ _(i) _(1,1) _(,s) ₂ _(i) _(1,2) _(,0) ⁽²⁾W_(s) ₁ _(i) _(1,1) _(,s) ₂ _(i) _(1,2) _(,s) ₁ _(i) _(1,1) _(,s) ₂ _(i)_(1,2) _(,1) ⁽²⁾ i₂′ 4 5 i_(1,1) _(, i) _(1,2) W_(s) ₁ _(i) _(1,1)_(+2p) ₁ _(,s) ₂ _(i) _(1,2) _(,s) ₁ _(i) _(1,1) _(+2p) ₁ _(,s) ₂ _(i)_(1,2) ⁽²⁾ W_(s) ₁ _(i) _(1,1) _(+2p) ₁ _(,s) ₂ _(i) _(1,2) _(,s) ₁ _(i)_(1,1) _(+2p) ₁ _(,s) ₂ _(i) _(1,2) _(,1) ⁽²⁾ i₂′ 8 9 i_(1,1) _(, i)_(1,2) W_(s) ₁ _(i) _(1,1) _(,s) ₂ _(i) _(1,2) _(,s) ₁ _(i) _(1,1) _(+p)₁ _(,s) ₂ _(i) _(1,2) _(,0) ⁽²⁾ W_(s) ₁ _(i) _(1,1) _(,s) ₂ _(i) _(1,2)_(,s) ₁ _(i) _(1,1) _(+p) ₁ _(,s) ₂ _(i) _(1,2) _(,1) ⁽²⁾ i₂′ 12 13i_(1,1) _(, i) _(1,2) W_(s) ₁ _(i) _(1,1) _(,s) ₂ _(i) _(1,2) _(,s) ₁_(i) _(1,1) _(+3p) ₁ _(,s) ₂ _(i) _(1,2) _(,0) ⁽²⁾ W_(s) ₁ _(i) _(1,1)_(,s) ₂ _(i) _(1,2) _(,s) ₁ _(i) _(1,1) _(+3p) ₁ _(,s) ₂ _(i) _(1,2)_(,1) ⁽²⁾ i₂′ 16 17 i_(1,1) _(, i) _(1,2) W_(s) ₁ _(i) _(1,1) _(,s) ₂_(i) _(1,2) _(+p) ₂ _(,s) ₁ _(i) _(1,1) _(,s) ₂ _(i) _(1,2) _(+p) ₂_(,0) ⁽²⁾ W_(s) ₁ _(i) _(1,1) _(,s) ₂ _(i) _(1,2) _(+p) ₂ _(,s) ₁ _(i)_(1,1) _(,s) ₂ _(i) _(1,2) _(+p) ₂ _(,1) ⁽²⁾ i₂′ 20 21 i_(1,1) _(, i)_(1,2) W_(s) ₁ _(i) _(1,1) _(+3p) ₁ _(,s) ₂ _(i) _(1,2) _(+p) ₂ _(,s) ₁_(i) _(1,1) _(+3p) ₁ _(,s) ₂ _(i) _(1,2) _(+p) ₂ _(,0) ⁽²⁾ W_(s) ₁ _(i)_(1,1) _(+3p) ₁ _(,s) ₂ _(i) _(1,2) _(+p) ₂ _(,s) ₁ _(i) _(1,1) _(+3p) ₁_(,s) ₂ _(i) _(1,2) _(+p) ₂ _(,1) ⁽²⁾ i₂′ 24 25 i_(1,1) _(, i) _(1,2)W_(s) ₁ _(i) _(1,1) _(+p) ₁ _(,s) ₂ _(i) _(1,2) _(+p) ₂ _(,s) ₁ _(i)_(1,1) _(+2p) ₁ _(,s) ₂ _(i) _(1,2) _(+p) ₂ _(,0) ⁽²⁾ W_(s) ₁ _(i)_(1,1) _(+p) ₁ _(,s) ₂ _(i) _(1,2) _(+p) ₂ _(,s) ₁ _(i) _(1,1) _(+2p) ₁_(,s) ₂ _(i) _(1,2) _(+p) ₂ _(,1) ⁽²⁾ i₂′ 28 29 i_(1,1) _(, i) _(1,2)W_(s) ₁ _(i) _(1,1) _(,s) ₂ _(i) _(1,2) _(,s) ₁ _(i) _(1,1) _(,s) ₂ _(i)_(1,2) _(+p) ₂ _(,0) ⁽²⁾ W_(s) ₁ _(i) _(1,1) _(,s) ₂ _(i) _(1,2) _(,s) ₁_(i) _(1,1) _(,s) ₂ _(i) _(1,2) _(+p) ₂ _(,1) ⁽²⁾ i₂′ 2 3 Precoder W_(s)₁ _(i) _(1,1) _(+p) ₁ _(,s) ₂ _(i) _(1,2) _(,s) ₁ _(i) _(1,1) _(+p) ₁_(,s) ₂ _(i) _(1,2) _(,0) ⁽²⁾ W_(s) ₁ _(i) _(1,1) _(+p) ₁ _(,s) ₂ _(i)_(1,2) _(,s) ₁ _(i) _(1,1) _(+p) ₁ _(,s) ₂ _(i) _(1,2) ₁ ⁽²⁾ i₂′ 6 7i_(1,1) _(, i) _(1,2) W_(s) ₁ _(i) _(1,1) _(+3p) ₁ _(,s) ₂ _(i) _(1,2)_(,s) ₁ _(i) _(1,1) _(+3p) ₁ _(,s) ₂ _(i) _(1,2) ₀ ⁽²⁾ W_(s) ₁ _(i)_(1,1) _(+3p) ₁ _(,s) ₂ _(i) _(1,2) _(,s) ₁ _(i) _(1,1) _(+3p) ₁ _(,s) ₂_(i) _(1,2) ₁ ⁽²⁾ i₂′ 10 11 i_(1,1) _(, i) _(1,2) W_(s) ₁ _(i) _(1,1)_(+p) ₁ _(,s) ₂ _(i) _(1,2) _(,s) ₁ _(i) _(1,1) _(+2p) ₁ _(,s) ₂ _(i)_(1,2) ₀ ⁽²⁾ W_(s) ₁ _(i) _(1,1) _(+p) ₁ _(,s) ₂ _(i) _(1,2) _(,s) ₁_(i) _(1,1) _(+2p) ₁ _(,s) ₂ _(i) _(1,2) ₁ ⁽²⁾ i₂′ 14 15 i_(1,1) _(, i)_(1,2) W_(s) ₁ _(i) _(1,1) _(+p) ₁ _(,s) ₂ _(i) _(1,2) _(,s) ₁ _(i)_(1,1) _(+3p) ₁ _(,s) ₂ _(i) _(1,2) ₀ ⁽²⁾ W_(s) ₁ _(i) _(1,1) _(+p) ₁_(,s) ₂ _(i) _(1,2) _(,s) ₁ _(i) _(1,1) _(+3p) ₁ _(,s) ₂ _(i) _(1,2) ₁⁽²⁾ i₂′ 18 19 i_(1,1) _(, i) _(1,2) W_(s) ₁ _(i) _(1,1) _(+p) ₁ _(,s) ₂_(i) _(1,2) _(+p) ₂ _(,s) ₁ _(i) _(1,1) _(+p) ₁ _(,s) ₂ _(i) _(1,2)_(+p) ₂ _(,0) ⁽²⁾ W_(s) ₁ _(i) _(1,1) _(+p) ₁ _(,s) ₂ _(i) _(1,2) _(+p)₂ _(,s) ₁ _(i) _(1,1) _(+p) ₁ _(,s) ₂ _(i) _(1,2) _(+p) ₂ _(,1) ⁽²⁾ i₂′22 23 i_(1,1) _(, i) _(1,2) W_(s) ₁ _(i) _(1,1) _(,s) ₂ _(i) _(1,2)_(+p) ₂ _(,s) ₁ _(i) _(1,1) _(+p) ₁ _(,s) ₂ _(i) _(1,2) _(+p) ₂ _(,0)⁽²⁾ W_(s) ₁ _(i) _(1,1) _(,s) ₂ _(i) _(1,2) _(+p) ₂ _(,s) ₁ _(i) _(1,1)_(+p) ₁ _(,s) ₂ _(i) _(1,2) _(+p) ₂ _(,1) ⁽²⁾ i₂′ 26 27 i_(1,1) _(, i)_(1,2) W_(s) ₁ _(i) _(1,1) _(+p) ₁ _(,s) ₂ _(i) _(1,2) _(+p) ₂ _(,s) ₁_(i) _(1,1) _(+3p) ₁ _(,s) ₂ _(i) _(1,2) _(+p) ₂ _(,0) ⁽²⁾ W_(s) ₁ _(i)_(1,1) _(+p) ₁ _(,s) ₂ _(i) _(1,2) _(+p) ₂ _(,s) ₁ _(i) _(1,1) _(+3p) ₁_(,s) ₂ _(i) _(1,2) _(+p) ₂ _(,1) ⁽²⁾ i₂′ 30 31 i_(1,1) _(, i) _(1,2)W_(s) ₁ _(i) _(1,1) _(+p) ₁ _(,s) ₂ _(i) _(1,2) _(,s) ₁ _(i) _(1,1)_(+p) ₁ _(,s) ₂ _(i) _(1,2) _(+p) ₂ _(,0) ⁽²⁾ W_(s) ₁ _(i) _(1,1) _(+p)₁ _(,s) ₂ _(i) _(1,2) _(,s) ₁ _(i) _(1,1) _(+p) ₁ _(,s) ₂ _(i) _(1,2)_(+p) ₂ _(,1) ⁽²⁾

For each Config value, the different possible values of i′₂ and theassociated values of s₁ and s₂ corresponding to the rank-2 Class Acodebook are given in Table 4.

In Table 4, two-dimensional beams are indicated by square shaped boxes.A square box with indices a′ b′ in the first dimension (e.g.,horizontal) and indices c′ d′ in the second dimension (e.g., vertical)corresponds to any codeword from Table 4 that satisfies the conditionsm₁=s₁i_(1,1)+a′, m₂=s₂i_(1,2)+c′, m′₁=s₁i_(1,1)+b′, andm′₂=s₂i_(1,2)+d′. For each Config value, the shaded, dashed and crossedboxes represent the two-dimensional beams that can be used to form theactive subset of codewords from the extended codebook table.

Rank-3 Class A Codebook

The rank-3 codebook can be defined in terms of four parameters: i_(1,1),i_(1,2), k and i′₂. The different parameter values of parameter krepresent different orthogonal beam groups. Each beam group consists ofL′₁ beams in the first dimension and L′₂ beams in the second dimensionwhere (L′₁, L′₂) are defined in Eq. 3. During feedback, the UE feedsback k as part of the W₁ indication. Each k value corresponds to onepair of (δ₁, δ₂) parameters as shown in Table 5. There can be twoalternatives for the maximum value of k:

-   -   Alt 1. Two values: k=0, 1 in Table 5    -   Alt 2. Maximum eight values:        -   If N₁>1 and N₂>1: k=0, 1, 2 . . . , 7 in Table 5        -   If N₂=1: k=0, 1, 2 in Table 5

TABLE 5 Mapping between k and (δ₁, δ₂) k δ 0 1 2 3 4 5 6 7 If N₁ > 1 andδ₁ O₁ 0 O₁ 2O₁ 0 O₁ 2O₁ 2O₁ N₂ > 1 δ₂ 0 O₂ O₂ 0 2O₂ 2O₂ O₂ 2O₂ If N₂ = 1δ₁ O₁ 2O₁ 3O₁ δ₂ 0 0 0

Furthermore, i_(1,1) and i_(1,2), are defined as:

i _(1,1)=0,1, . . . ,0₁ N ₁ /s ₁−1

i _(1,2)=0,1, . . . ,O ₂ N ₂ /s ₂−1.

Then, the rank-3 codebook can be defined as shown in Table 6. In Table6, the rank-3 codewords W_(m) ₁ _(,m) ₁ _(′) _(,m) ₂ _(,m) ₂ _(′) ⁽³⁾and {tilde over (W)}_(m) ₁ _(,m) ₁ _(′) _(,m) ₂ _(,m) ₂ _(′) ⁽³⁾ indexedby i′₂ are defined as:

$\begin{matrix}{{W_{m_{1},m_{1}^{\prime},m_{2},m_{2}^{\prime}}^{(3)} = {\frac{1}{\sqrt{3\; Q}}\begin{bmatrix}{v_{m_{1}} \otimes u_{m_{2}}} & {v_{m_{1}} \otimes u_{m_{2}}} & {v_{m_{1}^{\prime}} \otimes u_{m_{2}^{\prime}}} \\{v_{m_{1}} \otimes u_{m_{2}}} & {{- v_{m_{1}}} \otimes u_{m_{2}}} & {{- v_{m_{1}^{\prime}}} \otimes u_{m_{2}^{\prime}}}\end{bmatrix}}},} & \left( {{Eq}.\mspace{14mu} 8} \right) \\{{\overset{\sim}{W}}_{m_{1},m_{1}^{\prime},m_{2},m_{2}^{\prime}}^{(3)} = {{\frac{1}{\sqrt{3\; Q}}\begin{bmatrix}{v_{m_{1}} \otimes u_{m_{2}}} & {v_{m_{1}^{\prime}} \otimes u_{m_{2}^{\prime}}} & {v_{m_{1}^{\prime}} \otimes u_{m_{2}^{\prime}}} \\{v_{m_{1}} \otimes u_{m_{2}}} & {v_{m_{1}^{\prime}} \otimes u_{m_{2}^{\prime}}} & {{- v_{m_{1}^{\prime}}} \otimes u_{m_{2}^{\prime}}}\end{bmatrix}}.}} & \left( {{Eq}.\mspace{14mu} 9} \right)\end{matrix}$

For each Con fig value, the different possible values of i′₂ and theassociated values of (s₁, s₂) and (p₁, p₂) corresponding to the rank-3class A codebook are given in Table 7.

TABLE 6 Rank-3 Class A Codebook i₂′ 0 1 i_(1,1), W_(s) ₁ _(i) _(1,1)_(,s) ₁ _(i) _(1,1) _(+δ) ₁ _(,s) ₂ _(i) _(1,2) _(,s) ₂ _(i) _(1,2)_(+δ) ₂ ⁽³⁾ W_(s) ₁ _(i) _(1,1) _(+δ) ₁ _(,s) ₁ _(i) _(1,1) _(,s) ₂ _(i)_(1,2) _(+δ) ₂ _(,s) ₂ _(i) _(1,2) ⁽³⁾ i_(1,2), k i₂′ 4 5 i_(1,1), W_(s)₁ _(i) _(1,1) _(+p) ₁ _(,s) ₁ _(i) _(1,1) _(+p) ₁ _(+δ) ₁ _(,s) ₂ _(i)_(1,2) _(,s) ₂ _(i) _(1,2) ₊

⁽³⁾ W_(s) ₁ _(i) _(1,1) _(+p) ₁ _(+δ) ₁ _(,s) ₁ _(i) _(1,1) _(+p) ₁_(,s) ₂ _(i) _(1,2) _(+δ) ₂ _(,s) ₂ _(i) _(1,2) ⁽³⁾ i_(1,2), k i₂′ 8 9i_(1,1), W_(s) ₁ _(i) _(1,1) _(+2p) ₁ _(,s) ₁ _(i) _(1,1) _(+2p) ₁ _(+δ)₁ _(,s) ₂ _(i) _(1,2) _(,s) ₂ _(i) _(1,2) _(+δ) ₂ ⁽³⁾ W_(s) ₁ _(i)_(1,1) _(+2p) ₁ _(+δ) ₁ _(,s) ₁ _(i) _(1,1) _(+2p) ₁ _(,s) ₂ _(i) _(1,2)_(+δ) ₂ _(,s) ₂ _(i) _(1,2) ⁽³⁾ i_(1,2), k i₂′ 12 13 i_(1,1), W_(s) ₁_(i) _(1,1) _(+3p) ₁ _(,s) ₁ _(i) _(1,1) _(+3p) ₁ _(+δ) ₁ _(,s) ₂ _(i)_(1,2) _(,s) ₂ _(i) _(1,2) _(+δ) ₂ ⁽³⁾ W_(s) ₁ _(i) _(1,1) _(+3p) ₁_(+δ) ₁ _(,s) ₁ _(i) _(1,1) _(+3p) ₁ _(,s) ₂ _(i) _(1,2) _(+δ) ₂ _(,s) ₂_(i) _(1,2) ⁽³⁾ i_(1,2), k i₂′ 16-31 i_(1,1), Entries 16-31 constructedwith replacing s₂i_(1,2) in third and fourth subscripts i_(1,2), k withs₂i_(1,2) + p₂ in entries 0-15 i₂′ 2 3 i_(1,1), {tilde over (W)}_(s) ₁_(i) _(1,1) _(,s) ₁ _(i) _(1,1) _(+δ) ₁ _(,s) ₂ _(i) _(1,2) _(,s) ₂ _(i)_(1,2) _(+δ) ₂ ⁽³⁾ {tilde over (W)}_(s) ₁ _(i) _(1,1) _(+δ) ₁ _(,s) ₁_(i) _(1,1) _(,s) ₂ _(i) _(1,2) _(+δ) ₂ _(,s) ₂ _(i) _(1,2) ⁽³⁾ i_(1,2),k i₂′ 6 7 i_(1,1), {tilde over (W)}_(s) ₁ _(i) _(1,1) _(+p) ₁ _(,s) ₁_(i) _(1,1) _(+p) ₁ _(+δ) ₁ _(,s) ₂ _(i) _(1,2) _(,s) ₂ _(i) _(1,2)_(+δ) ₂ ⁽³⁾ {tilde over (W)}_(s) ₁ _(i) _(1,1) _(+p) ₁ _(+δ) ₁ _(,s) ₁_(i) _(1,1) _(+p) ₁ _(,s) ₂ _(i) _(1,2) _(+δ) ₂ _(,s) ₂ _(i) _(1,2) ⁽³⁾i_(1,2), k i₂ ₁ _(,s) ₁ _(′) 10 11 i_(1,1), {tilde over (W)}_(s) ₁ _(i)_(1,1) _(+2p) ₁ _(,s) ₁ _(i) _(1,1) _(+2p) ₁ _(+δ) ₁ _(,s) ₂ _(i) _(1,2)_(,s) ₂ _(i) _(1,2) _(+δ) ₂ ⁽³⁾ {tilde over (W)}_(s) ₁ _(i) _(1,1)_(+2p) ₁ _(+δ) ₁ _(,s) ₁ _(i) _(1,1) _(+2p) ₁ _(,s) ₂ _(i) _(1,2) _(+δ)₂ _(,s) ₂ _(i) _(1,2) ⁽³⁾ i_(1,2), k i₂′ 14 15 i_(1,1), {tilde over(W)}_(s) ₁ _(i) _(1,1) _(+3p) ₁ _(,s) ₁ _(i) _(1,1) _(+3p) ₁ _(+δ) ₁_(,s) ₂ _(i) _(1,2) _(,s) ₂ _(i) _(1,2) _(+δ) ₂ ⁽³⁾ {tilde over (W)}_(s)₁ _(i) _(1,1) _(+3p) ₁ _(+δ) ₁ _(,s) ₁ _(i) _(1,1) _(+3p) ₁ _(,s) ₂ _(i)_(1,2) _(+δ) ₂ _(,s) ₂ _(i) _(1,2) ⁽³⁾ i_(1,2), k i₂′ 16-31 i_(1,1),Entries 16-31 constructed with replacing s₂i_(1,2) in third and fourthsubscripts i_(1,2), k with s₂i_(1,2) + p₂ in entries 0-15

indicates data missing or illegible when filed

TABLE 7 Selection of i₂ ^(′) , (s₁, s₂), and (p₁, p₂) for Rank-3 Class ACodebook Config Selected i₂ ^(′) indices (s₁, s₂) (p₁, p₂) 1 0, 2 (1, 1)(−, −) 2 0-7, 16-23 (O₁, O₂)$\left( {\frac{O_{1}}{2},\frac{O_{2}}{2}} \right)$ 3 0-3, 8-11, 20- 23,28-31 (O₁, O₂) $\left( {\frac{O_{1}}{4},\frac{O_{2}}{2}} \right)$ 4 0-15$\left( {O_{1},\frac{O_{2}}{2}} \right)$$\left( {\frac{O_{1}}{4}, -} \right)$

Rank-4 Class A Codebook

The rank-4 codebook can be defined in terms of four parameters: i_(1,1),i_(1,2), k and i′₂. The different parameter values of parameter krepresent different orthogonal beam groups. Each beam group consists ofL′₁ beams in the first dimension and L′₂ beams in the second dimension,where (L′₁, L′₂) are defined in Eq. 3. During feedback, the UE feedsback k as part of the W₁ indication. Each k value corresponds to onepair of (δ₁, δ₂) parameters as shown in Table 5. There can be twoalternatives for the maximum value of k:

-   -   Alt 1. Two values: k=0, 1 in Table 5    -   Alt 2. Maximum eight values:        -   If N₁>1 and N₂>1: k=0, 1, 2 . . . , 7 in Table 5        -   If N₂=1: k=0, 1, 2 in Table 5

Furthermore, i_(1,1) and i_(1,2), are defined as:

i _(1,1)=0,1, . . . ,0₁ N ₁ /s ₁−1

i _(1,2)=0,1, . . . ,O ₂ N ₂ /s ₂−1.

Then, the rank-4 codebook can be defined as shown in Table 8. In Table8, the rank-4 codewords W_(m) ₁ _(,m) ₁ _(′) _(,m) ₂ _(,m) ₂ _(′) _(,n)⁽⁴⁾ indexed by i′₂ are defined as:

                                       (Eq.  10)$W_{m_{1},m_{1}^{\prime},m_{2},m_{2}^{\prime},n}^{(4)} = {{\frac{1}{\sqrt{4\; Q}}\begin{bmatrix}{v_{m_{1}} \otimes u_{m_{2}}} & {v_{m_{1}^{\prime}} \otimes u_{m_{2}^{\prime}}} & {v_{m_{1}} \otimes u_{m_{2}}} & {v_{m_{1}^{\prime}} \otimes u_{m_{2}^{\prime}}} \\{\phi_{n}{v_{m_{1}} \otimes u_{m_{2}}}} & {\phi_{n}{v_{m_{1}^{\prime}} \otimes u_{m_{2}^{\prime}}}} & {{- \phi_{n}}{v_{m_{1}} \otimes u_{m_{2}}}} & {{- \phi_{n}}{v_{m_{1}^{\prime}} \otimes u_{m_{2}^{\prime}}}}\end{bmatrix}}.}$

For each Config value, the different possible values of i′₂ and theassociated values of (s₁, s₂) and (p₁, p₂) corresponding to the rank-4class A codebook are given in Table 9.

TABLE 8 Rank-4 Class A Codebook i₂′ 0 1 i_(1,1), W_(s) ₁ _(i) _(1,1)_(,s) ₁ _(i) _(1,1) _(+δ) ₁ _(,s) ₂ _(i) _(1,2) _(,s) ₂ _(i) _(1,2)_(+δ) ₂ _(,0) ⁽⁴⁾ W_(s) ₁ _(i) _(1,1) _(s) ₁ _(i) _(1,1) _(+δ) ₁ _(,s) ₂_(i) _(1,2) _(,s) ₂ _(i) _(1,2) _(+δ) ₂ _(,1) ⁽⁴⁾ i_(1,2), k i₂′ 4 5i_(1,1), W_(s) ₁ _(i) _(1,1) _(+2p) ₁ _(,s) ₁ _(i) _(1,1) _(+2p) ₁ _(+δ)₁ _(,s) ₂ _(i) _(1,2) _(,s) ₂ _(i) _(1,2) _(+δ) ₂ ⁽⁴⁾ W_(s) ₁ _(i)_(1,1) _(+2p) ₁ _(,s) ₁ _(i) _(1,1) _(+2p) ₁ _(+δ) ₁ _(,s) ₂ _(i) _(1,2)_(,s) ₂ _(i) _(1,2) _(+δ) ₂ _(,1) ⁽⁴⁾ i_(1,2), k i₂′ 8-15 i_(1,1),Entries 8-15 constructed with replacing s₂i_(1,2) in third and fourthsubscripts with s₂i_(1,2) + p₂ in i_(1,2), k entries 0-7 i₂′ 2 3i_(1,1), W_(s) ₁ _(i) _(1,1) _(+p) ₁ _(,s) ₁ _(i) _(1,1) _(+p) ₁ _(+δ) ₁_(,s) ₂ _(i) _(1,2) _(,s) ₂ _(i) _(1,2) _(+δ) ₂ _(,0) ⁽⁴⁾ W_(s) ₁ _(i)_(1,1) _(+p) ₁ _(,s) ₁ _(i) _(1,1) _(+p) ₁ _(+δ) ₁ _(,s) ₂ _(i) _(1,2)_(,s) ₂ _(i) _(1,2) _(+δ) ₂ _(,1) ⁽⁴⁾ i_(1,2), k i₂′ 6 7 i_(1,1), W_(s)₁ _(i) _(1,1) _(+3p) ₁ _(,s) ₁ _(i) _(1,1) _(+3p) ₁ _(+δ) ₁ _(,s) ₂ _(i)_(1,2) _(,s) ₂ _(i) _(1,2) _(+δ) ₂ _(,0) ⁽⁴⁾ W_(s) ₁ _(i) _(1,1) _(+3p)₁ _(,s) ₁ _(i) _(1,1) _(+3p) ₁ _(+δ) ₁ _(,s) ₂ _(i) _(1,2) _(,s) ₂ _(i)_(1,2) _(+δ) ₂ _(,1) ⁽⁴⁾ i_(1,2), k i₂′ 8-15 i_(1,1), Entries 8-15constructed with replacing s₂i_(1,2) in third and fourth subscripts withs₂i_(1,2) + p₂ in i_(1,2), k entries 0-7

TABLE 9 Selection of i₂′, (s₁, s₂), and (p₁, p₂) for Rank-4 Class ACodebook Config Selected i₂′ indices (s₁, s₂) (p₁, p₂) 1 0, 1 (1, 1) (—,—) 2 0-3, 8-11 (O₁, O₂)$\left( {\frac{O_{1}}{2},\frac{O_{2}}{2}} \right)$ 3 0-1, 4-5, 10-11,14-15 (O₁, O₂) $\left( {\frac{O_{1}}{4},\frac{O_{2}}{2}} \right)$ 4 0-7$\left( {O_{1},\frac{O_{2}}{2}} \right)$$\left( {\frac{O_{1}}{4}, -} \right)$

Ranks 5-8 Class A Codebooks

For ranks 5-8, the Class A codebooks are defined by two parameters:{i₁₁, i₁₂}. The i_(1,1) and i_(1,2) parameters are defined as:

i _(1,1)=0,1, . . . ,0₁ N ₁ /s ₁−1

i _(1,2)=0,1, . . . ,O ₂ N ₂ /s ₂−1.

For a given Config, (s₁, s₂) values are determined similar to Table 9. Aprecoding matrix codeword for rank r (r=5, 6, 7, 8) is denoted as W_(i)_(1,1) _(,i) _(1,2) ^((r)). The precoding matrix codewords W_(i) _(1,1)_(,i) _(1,2) ^((r)), r=5, 6, 7, 8 are then defined as:

                                                                                   (Eq.  11)${W_{i_{1,1},i_{1,2}}^{(5)} = {\frac{1}{\sqrt{5\; Q}}\begin{bmatrix}{v_{s_{1},i_{1,1}} \otimes u_{s_{2}i_{1,2}}} & {v_{s_{1},i_{1,1}} \otimes u_{s_{2}i_{1,2}}} & {v_{{s_{1}i_{1,1}} + \delta_{1,1}} \otimes u_{{s_{2}i_{1,2}} + \delta_{2,1}}} & {v_{{s_{1}i_{1,1}} + \delta_{1,1}} \otimes u_{{s_{2}i_{1,2}} + \delta_{2,1}}} & {v_{{s_{1}i_{1,1}} + \delta_{1,2}} \otimes u_{{s_{2}i_{1,2}} + \delta_{2,2}}} \\{v_{s_{1},i_{1,1}} \otimes u_{s_{2}i_{1,2}}} & {{- v_{s_{1},i_{1,1}}} \otimes u_{s_{2}i_{1,2}}} & {v_{{s_{1}i_{1,1}} + \delta_{1,1}} \otimes u_{{s_{2}i_{1,2}} + \delta_{2,1}}} & {{- v_{{s_{1}i_{1,1}} + \delta_{1,1}}} \otimes u_{{s_{2}i_{1,2}} + \delta_{2,1}}} & {v_{{s_{1}i_{1,1}} + \delta_{1,2}} \otimes u_{{s_{2}i_{1,2}} + \delta_{2,2}}}\end{bmatrix}}},\mspace{1490mu} {{Eq}.\mspace{14mu} 12}$$W_{i_{1,1},i_{1,2}}^{(6)} = {\frac{1}{\sqrt{6\; Q}}{\quad{\begin{bmatrix}{v_{s_{1}i_{1,1}} \otimes u_{s_{2}i_{1,2}}} & {v_{s_{1}i_{1,1}} \otimes u_{s_{2}i_{1,2}}} & {v_{{s_{1}i_{1,1}} + \delta_{1,1}} \otimes u_{{s_{2}i_{1,2}} + \delta_{2,1}}} & {v_{{s_{1}i_{1,1}} + \delta_{1,1}} \otimes u_{{s_{2}i_{1,2}} + \delta_{2,1}}} & {v_{{s_{1}i_{1,1}} + \delta_{1,2}} \otimes u_{{s_{2}i_{1,2}} + \delta_{2,2}}} & {v_{{s_{1}i_{1,1}} + \delta_{1,2}} \otimes u_{{s_{2}i_{1,2}} + \delta_{2,2}}} \\{v_{s_{1}i_{1,1}} \otimes u_{s_{2}i_{1,2}}} & {{- v_{s_{1}i_{1,1}}} \otimes u_{s_{2}i_{1,2}}} & {v_{{s_{1}i_{1,1}} + \delta_{1,1}} \otimes u_{{s_{2}i_{1,2}} + \delta_{2,1}}} & {{- v_{{s_{1}i_{1,1}} + \delta_{1,1}}} \otimes u_{{s_{2}i_{1,2}} + \delta_{2,1}}} & {v_{{s_{1}i_{1,1}} + \delta_{1,2}} \otimes u_{{s_{2}i_{1,2}} + \delta_{2,2}}} & {{- v_{{s_{1}i_{1,1}} + \delta_{1,2}}} \otimes u_{{s_{2}i_{1,2}} + \delta_{2,2}}}\end{bmatrix},\mspace{1490mu} {{{{Eq}.\mspace{14mu} 13}W_{i_{1,1},i_{1,2}}^{(7)}} = {\frac{1}{\sqrt{7\; Q}}{\quad{\begin{bmatrix}{v_{s_{1}i_{1,1}} \otimes u_{s_{2}i_{1,2}}} & {v_{s_{1}i_{1,1}} \otimes u_{s_{2}i_{1,2}}} & {v_{{s_{1}i_{1,1}} + \delta_{1,1}} \otimes u_{{s_{2}i_{1,2}} + \delta_{2,1}}} & {v_{{s_{1}i_{1,1}} + \delta_{1,1}} \otimes u_{{s_{2}i_{1,2}} + \delta_{2,1}}} & \begin{matrix}{v_{{s_{1}i_{1,1}} + \delta_{1,2}} \otimes} \\u_{{s_{2}i_{1,2}} + \delta_{2,2}}\end{matrix} & \begin{matrix}{v_{{s_{1}i_{1,1}} + \delta_{1,2}} \otimes} \\u_{{s_{2}i_{1,2}} + \delta_{2,2}}\end{matrix} & \begin{matrix}{v_{{s_{1}i_{1,1}} + \delta_{1,3}} \otimes} \\u_{{s_{2}i_{1,2}} + \delta_{2,3}}\end{matrix} \\{v_{s_{1}i_{1,1}} \otimes u_{s_{2}i_{1,2}}} & {{- v_{s_{1}i_{1,1}}} \otimes u_{s_{2}i_{1,2}}} & {v_{{s_{1}i_{1,1}} + \delta_{1,1}} \otimes u_{{s_{2}i_{1,2}} + \delta_{2,1}}} & {{- v_{{s_{1}i_{1,1}} + \delta_{1,1}}} \otimes u_{{s_{2}i_{1,2}} + \delta_{2,1}}} & \begin{matrix}{v_{{s_{1}i_{1,1}} + \delta_{1,2}} \otimes} \\u_{{s_{2}i_{1,2}} + \delta_{2,2}}\end{matrix} & \begin{matrix}{{- v_{{s_{1}i_{1,1}} + \delta_{1,2}}} \otimes} \\u_{{s_{2}i_{1,2}} + \delta_{2,2}}\end{matrix} & \begin{matrix}{v_{{s_{1}i_{1,1}} + \delta_{1,3}} \otimes} \\u_{{s_{2}i_{1,2}} + \delta_{2,3}}\end{matrix}\end{bmatrix},\mspace{1490mu} {{{{Eq}.\mspace{14mu} 14}W_{i_{1,1},i_{1,2}}^{(8)}} = {\frac{1}{\sqrt{8\; Q}}{\quad\begin{bmatrix}{v_{s_{1}i_{1,1}} \otimes u_{s_{2}i_{1,2}}} & {v_{s_{1}i_{1,1}} \otimes u_{s_{2}i_{1,2}}} & \begin{matrix}{v_{{s_{1}i_{1,1}} + \delta_{1,1}} \otimes} \\u_{{s_{2}i_{1,2}} + \delta_{2,1}}\end{matrix} & \begin{matrix}{v_{{s_{1}i_{1,1}} + \delta_{1,1}} \otimes} \\u_{{s_{2}i_{1,2}} + \delta_{2,1}}\end{matrix} & \begin{matrix}{v_{{s_{1}i_{1,1}} + \delta_{1,2}} \otimes} \\u_{{s_{2}i_{1,2}} + \delta_{2,2}}\end{matrix} & \begin{matrix}{v_{{s_{1}i_{1,1}} + \delta_{1,2}} \otimes} \\u_{{s_{2}i_{1,2}} + \delta_{2,2}}\end{matrix} & \begin{matrix}{v_{{s_{1}i_{1,1}} + \delta_{1,3}} \otimes} \\u_{{s_{2}i_{1,2}} + \delta_{2,3}}\end{matrix} & \begin{matrix}{v_{{s_{1}i_{1,1}} + \delta_{1,3}} \otimes} \\u_{{s_{2}i_{1,2}} + \delta_{2,3}}\end{matrix} \\{v_{s_{1}i_{1,1}} \otimes u_{s_{2}i_{1,2}}} & {{- v_{s_{1}i_{1,1}}} \otimes u_{s_{2}i_{1,2}}} & \begin{matrix}{v_{{s_{1}i_{1,1}} + \delta_{1,1}} \otimes} \\u_{{s_{2}i_{1,2}} + \delta_{2,1}}\end{matrix} & \begin{matrix}{{- v_{{s_{1}i_{1,1}} + \delta_{1,1}}} \otimes} \\u_{{s_{2}i_{1,2}} + \delta_{2,1}}\end{matrix} & \begin{matrix}{v_{{s_{1}i_{1,1}} + \delta_{1,2}} \otimes} \\u_{{s_{2}i_{1,2}} + \delta_{2,2}}\end{matrix} & \begin{matrix}{{- v_{{s_{1}i_{1,1}} + \delta_{1,2}}} \otimes} \\u_{{s_{2}i_{1,2}} + \delta_{2,2}}\end{matrix} & \begin{matrix}{v_{{s_{1}i_{1,1}} + \delta_{1,3}} \otimes} \\u_{{s_{2}i_{1,2}} + \delta_{2,3}}\end{matrix} & \begin{matrix}{{- v_{{s_{1}i_{1,1}} + \delta_{1,3}}} \otimes} \\u_{{s_{2}i_{1,2}} + \delta_{2,3}}\end{matrix}\end{bmatrix}}}}}}}}}}}$

For sixteen ports (i.e., N₁N₂=8), δ_(1,1), δ_(1,2), δ_(1,3), δ_(2,1),δ_(2,2), δ_(2,3) are defined as in Table 10. For twelve ports (i.e.,N₁N₂=6), δ_(1,1), δ_(1,2), δ_(1,3), δ_(2,1), δ_(2,2), δ_(2,3) aredefined as in Table 12.

TABLE 10 Delta values for cases with 16 ports and ranks 5-8 Antennaconfiguration δ_(1,1) δ_(2,1) δ_(1,2) δ_(2,2) δ_(1,3) δ_(2,3) Config = 4N₁ ≥ N₂ O₁ 0 2O₁ 0 3O₁ 0 N₁ < N₂ 0 O₂ 0 2O₂ 0 3O₂ Config = 3 N₁ ≥ N₂ O₁0 2O₁ O₂ 3O₁ O₂ N₁ < N₂ 0 O₂ O₁ 2O₂ O₁ 3O₂ Config = 2 Both O₁ 0 O₁ O₂ 0O₂

TABLE 11 Delta values for cases with 12 ports and ranks 5-8 TypeConfiguration δ_(1,1) δ_(2,1) δ_(1,2) δ_(2,2) δ_(1,3) δ_(2,3) Config = 4N₁ ≥ N₂ O₁ 0 2O₁ 0 0 O₂ N₁ < N₂ 0 O₂ 0 2O₂ O₁ 0 Config = 3 N₁ ≥ N₂ O₁ 0O₁ O₂ 2O₁ O₂ N₁ < N₂ 0 O₂ O₁ O₂ O₁ 2O₂ Config = 2 Both O₁ 0 O₁ O₂ 0 O₂

Codebook Subset Restriction

Codebook subset restriction (CSR) is supported in LTE, as of Release 12of the 3GPP specifications, and is described in 3GPP TS 36.213 V12.3.0and 3GPP TS 36.331 V12.3.0. With codebook subset restriction, a subsetof the precoders in the codebook is restricted so that the UE has asmaller set of possible precoders to choose from. This effectivelyreduces the size of the codebook implying that the search for the bestPMI can be done on the smaller unrestricted set of precoders, therebyalso reducing the UE computational requirements for this particularsearch. Typically, the eNodeB would signal the codebook subsetrestriction to the UE by means of a bitmap in a dedicated message partof the AntennaInfo information element, one bit for each precoder in thecodebook, where a 1 indicates that the precoder is restricted, meaningthat the UE is not allowed to choose and report the precoder. Thus, fora codebook with A_(c) different codewords across all ranks, a bitmap oflength A_(c) would be used to signal the codebook subset restriction.The number of bits A_(c) associated with different codebooks fordifferent transmission modes is shown in Table 12 below. This allows forfull flexibility for the eNodeB to restrict every possible subset of thecodebook. There are thus 2^(A) ^(c) possible codebook subset restrictionconfigurations. For large antenna arrays with many antenna elements, theeffective beams become narrow and a codebook containing many precodersis required for the intended coverage area. Furthermore, fortwo-dimensional antenna arrays, the codebook size increasesquadratically since the precoders in the codebook need to span twodimensions, typically the horizontal and vertical domain. Thus, thecodebook size, i.e. the total number of possible precoding matrices W,can be very large. Signaling a codebook subset restriction in the LTEpre-release-13 way, by means of a bitmap with one bit for everyprecoder, can thus impose a large overhead, especially if the codebooksubset restriction (CSR) is frequently updated or if there are manyusers served by the cell where each UE has to receive the CSR.

TABLE 12 Number of bits in codebook subset restriction bitmap forapplicable transmission modes Number of bits A_(c) 2 antenna 8 antennaports 4 antenna ports ports Transmission 2  4 mode 3 Transmission 6 64mode 4 Transmission 4 16 mode 5 Transmission 4 16 mode 6 Transmission 664 with mode 8 alternativeCodeBookEnabledFor4TX- r12 = TRUE configured,otherwise 32 Transmission 6 96 with 109 modes 9alternativeCodeBookEnabledFor4TX- and 10 r12 = TRUE configured,otherwise 64

To address the shortcomings of the legacy CSR, two-dimensionalbeam-based codebook subset restriction will be implemented in LTERel-13. Let (l₁, l₂) denote the two-dimensional beam in X₁⊗X₂corresponding to the l₁ ^(th) DFT vector in the first dimension, e.g.,horizontal dimension, and l₂ ^(th) DFT vector in the second dimension,e.g., vertical dimension. Then, codebook subset restriction (CSR) issupported for FD-MIMO, where:

-   -   CSR is configured via RRC signaling    -   A subset of two-dimensional beams (l₁, l₂) are forbidden, i.e.,        not allowed to be reported according to the CSR configuration        -   A forbidden two-dimensional beam is not allowed in reporting            with any rank    -   Rank restriction is also supported    -   CSR can be also applied to W₂    -   Number of PMI bits does not vary according to restricted subset        -   Note: Codebook subset restriction targets e.g.            performance/capacity, as in Rel-8 to Rel-12

It has been further agreed that

-   -   For W₁ CSR, a bitmap of (N₁O₁N₂O₂) bits indicates a        two-dimensional-beams subset restriction; this bitmap is        referred to as Beam-Subset-Restriction in the rest of this        document.    -   an additional 8-bit bitmap indicates rank restriction; this        bitmap is referred to as Rank-Restriction in the rest of this        document.    -   and a RRC parameter for CSR on Class A i2 (i.e., W₂) will be        introduced; this parameter, which takes the form of another        bitmap, will be referred to as i2-Subset-Restriction in the rest        of this document.

SUMMARY

Although the RRC signaling of the Beam-Subset-Restriction bitmap, thei2-Subset-Restriction bitmap, and/or a Rank-Restriction bitmap areagreed, the exact details on how these bitmaps should be used to achievecodebook subset restriction at the user equipment (UE) for LTE Release13 are still not specified. A remaining problem is how to utilize theagreed bitmaps to achieve codebook subset restriction for Release 13, toinclude both two-dimensional beam restriction and rank restriction.

It is an object of embodiments described herein to address this problem.It is possible to achieve this object and others by using methods andapparatuses, such as radio network nodes and wireless devices, asdescribed herein.

According to one aspect, there are provided methods performed by/in aradio network node for configuring a wireless device in a wirelessnetwork. An example method comprises identifying, among a predeterminedcodebook of precoding matrix codewords, a subset of precoding matrixcodewords that are not to be reported by the wireless device inchannel-state-information (CSI) feedback. The method further comprisestransmitting, to the wireless device, a bitmap identifying the subset ofprecoding matrix codewords that are not to be reported by the wirelessdevice. Each bit in the bitmap corresponds to only one combination of afirst dimension index l′₁ and a second dimension index l′₂ out of thepossible combinations of the first dimension index l′₁ and the seconddimension index l′₂, where the first dimension index l′₁ and the seconddimension index l′₂ identify a two-dimensional beam, the two-dimensionalbeam being defined by a vector of complex numbers comprised within atleast one column of a precoding matrix codeword in the codebook. In someembodiments, the first dimension index l′₁ and the second dimensionindex l′₂ may be first and second forbidden dimension indices,respectively, such that the first dimension index l′₁ and the seconddimension index l′₂ identify a forbidden two-dimensional beam for whichcorresponding precoding matrix codewords are not to be reported.

According to another aspect, there is provided a radio network node forconfiguring a wireless device in a wireless network, the radio networknode comprising processing circuitry and a memory, the memory containinginstructions executable by the processing circuitry, whereby the radionetwork node is adapted and/or configured and/or operative to identify,among a predetermined codebook of precoding matrix codewords, a subsetof precoding matrix codewords that are not to be reported by thewireless device in channel-state-information (CSI) feedback, and totransmit, to the wireless device, a bitmap identifying the subset ofprecoding matrix codewords that are not to be reported by the wirelessdevice. Again, each bit in the bitmap corresponds to only onecombination of a first dimension index l′₁ and a second dimension indexl′₂ out of the possible combinations of the first dimension index l′₁and the second dimension index l′₂, where the first dimension index l′₁and the second dimension index l′₂ identify a two-dimensional beam, thetwo-dimensional beam being defined by a vector of complex numberscomprised within at least one column of a precoding matrix codeword inthe codebook. Again, in some embodiments, the first dimension index l′₁and the second dimension index l′₂ may be first and second forbiddendimension indices, respectively, such that the first dimension index l′₁and the second dimension index l′₂ identify a forbidden two-dimensionalbeam for which corresponding precoding matrix codewords are not to bereported.

According to a third aspect, there are provided methods, by/in awireless device operating in a wireless network. An example methodcomprises receiving, from a radio network node, a bitmap indicating,among a predetermined codebook of precoding matrix codewords, a subsetof precoding matrix codewords that are not to be reported by thewireless device in channel-state-information (CSI) feedback. The methodfurther comprises identifying, using the bitmap, the subset of precodingmatrix codewords that are not to be reported by the wireless device inCSI feedback. Each bit in the bitmap corresponds to only one combinationof a first dimension index l′₁ and a second dimension index l′₂ out ofthe possible combinations of the first dimension index l′₁ and thesecond dimension index l′₂, where the first dimension index l′₁ and thesecond dimension index l′₂ identify a two-dimensional beam, thetwo-dimensional beam being defined by a vector of complex numberscomprised within at least one column of a precoding matrix codeword inthe codebook. Once more, in some embodiments, the first dimension indexl′₁ and the second dimension index l′₂ may be first and second forbiddendimension indices, respectively, such that the first dimension index l′₁and the second dimension index l′₂ identify a forbidden two-dimensionalbeam for which corresponding precoding matrix codewords are not to bereported.

According to a fourth aspect, there is provided a wireless device,comprising processing circuitry and a memory, the memory containinginstructions executable by the processing circuitry, whereby thewireless device is adapted and/or configured and/or operative toreceive, from a radio network node, a bitmap indicating, among apredetermined codebook of precoding matrix codewords, a subset ofprecoding matrix codewords that are not to be reported by the wirelessdevice in channel-state-information (CSI) feedback; and to identify,using the bitmap, the subset of precoding matrix codewords that are notto be reported by the wireless device in CSI feedback. Once more, eachbit in the bitmap corresponds to only one combination of a firstdimension index l′₁ and a second dimension index l′₂ out of the possiblecombinations of the first dimension index l′₁ and the second dimensionindex l′₂, where the first dimension index l′₁ and the second dimensionindex l′₂ identify a two-dimensional beam, the two-dimensional beambeing defined by a vector of complex numbers comprised within at leastone column of a precoding matrix codeword in the codebook. As above, insome embodiments, the first dimension index l′₁ and the second dimensionindex l′₂ may be first and second forbidden dimension indices,respectively, such that the first dimension index l′₁ and the seconddimension index l′₂ identify a forbidden two-dimensional beam for whichcorresponding precoding matrix codewords are not to be reported.

The above wireless device and radio network node and methods therein maybe implemented and configured according to different optionalembodiments to accomplish further features and benefits, to be describedbelow.

Some of the advantages achieved by the techniques described herein are:

-   -   The disclosed techniques provide detailed solutions for how to        apply beam restriction across ranks using the agreed        Beam-Subset-Restriction bitmap.    -   The disclosed techniques provide detailed solutions for mapping        between the bits in Beam-Subset-Restriction bitmap and the        two-dimensional beams.    -   The disclosed techniques resolve any ambiguity regarding the        order in or priority with which different restriction signals        should be applied when multiple bitmaps, i.e.,        Beam-Subset-Restriction bitmap, i2-Subset-Restriction bitmap,        and/or Rank-Restriction bitmap, are RRC signaled to the UE.

BRIEF DESCRIPTION OF FIGURES

The presently disclosed methods and apparatus will now be described inmore detail by means of exemplary embodiments and with reference to theaccompanying figures, in which:

FIG. 1 illustrates an example of an LTE downlink physical resource.

FIG. 2 illustrates an example of an LTE time-domain (frame) structure.

FIG. 3 illustrates an LTE downlink subframe with three OFDM symbols forlower layer control signaling, in particular DCI messages

FIG. 4 illustrates the transmission structure of precodedspatial-multiplexing mode in LTE.

FIG. 5 illustrates an example antenna array and an array ofcorresponding antenna ports.

FIG. 6 illustrates an exemplary wireless network 100 in whichembodiments herein may be applied and/or implemented.

FIG. 7 illustrates a “second-dimension-first” approach to mappingbetween the Beam-Subset-Restriction bits and two-dimensional beams.

FIG. 8 illustrates an example of “second-dimension-first” mapping.

FIG. 9 illustrates a “first-dimension-first” approach to mapping betweenthe Beam-Subset-Restriction bits and two-dimensional beams.

FIG. 10 illustrates an example of “first-dimension-first” mapping.

FIG. 11 illustrates a method performed in a radio network node 80according to embodiments herein.

FIG. 12 illustrates a method performed in a wireless device 90 accordingto embodiments herein.

FIG. 13 is a block diagram illustrating a radio network node 80,according to exemplary embodiments herein.

FIG. 14 is a block diagram illustrating a wireless device 90, accordingto exemplary embodiments herein.

DETAILED DESCRIPTION

The following description with reference to the accompanying drawings isprovided to assist in a comprehensive understanding of exemplaryembodiments of the invention as defined by the enumerated exampleembodiments provided below, and their equivalents. It includes variousspecific details to assist in that understanding but these are to beregarded as merely exemplary. Accordingly, those of ordinary skill inthe art will recognize that various changes and modifications of theembodiments described herein can be made without departing from thescope of the invention. Also, descriptions of well-known functions andconstructions are omitted for clarity and conciseness. Accordingly, itshould be apparent to those skilled in the art that the followingdescription of exemplary embodiments of the present invention areprovided for illustration purpose only and not for the purpose oflimiting the invention as defined by the appended enumerated exampleembodiments and their equivalents. It is to be understood that thesingular forms “a,” “an,” and “the” include plural referents unless thecontext clearly dictates otherwise. Thus, for example, reference to “acomponent surface” includes reference to one or more of such surfaces.

As used herein, the non-limiting terms “wireless device” and “UserEquipment,” or UE,” may refer to a mobile phone, a cellular phone, aPersonal Digital Assistant, PDA, equipped with radio communicationcapabilities, a smart phone, a laptop or Personal Computer, PC, equippedwith an internal or external mobile broadband modem, a tablet PC withradio communication capabilities, a target device, a device to deviceUE, a machine type UE or UE capable of machine to machine communication,iPAD, customer premises equipment, CPE, laptop embedded equipment, LEE,laptop mounted equipment, LME, Universal Serial Bus (USB) dongle, aportable electronic radio communication device, a sensor device equippedwith radio communication capabilities or the like. In particular, theterm “wireless device” should be interpreted as a non-limiting termcomprising any type of wireless device communicating with a radionetwork node in a cellular or mobile communication system or any deviceequipped with radio circuitry for wireless communication according toany relevant standard for communication within a cellular or mobilecommunication system.

As used herein, the non-limiting term “radio network node” may refer tobase stations, network control nodes such as network controllers, radionetwork controllers, base station controllers, and the like. Inparticular, the term “base station” may encompass different types ofradio base stations including standardized base stations such as NodeBs, or evolved Node Bs, eNBs, for LTE.

In the present disclosure, the non-limiting term “wireless network” mayrefer to any radio communication networks, in particular UniversalTerrestrial Radio Access (UTRA) for Wideband Code Division MultipleAccess (WCDMA) or Evolved Universal Terrestrial Radio Access (E-UTRA)for LTE, but any other wireless communications system such as WiFi andWiMax can be anticipated. Although terminology from 3GPP LTE is used inthis disclosure to exemplify the inventive techniques and apparatus,this should not be seen as limiting the scope of the disclosedtechniques and apparatus to only the aforementioned system. Otherwireless systems, including WCDMA, WiFi, WiMax, LTE for unlicensed band,Ultra Mobile Broadband (UMB (and GSM, may also benefit from exploitingthe ideas covered within this disclosure.

Also note that terminology such as eNodeB and UE should be consideringnon-limiting and does in particular not imply a certain hierarchicalrelation between the two; in general “eNodeB” or Transmission Point (TP)could be considered as device 1 and “UE” device 2, and these two devicescommunicate with each other over some radio channel. Herein, we focus onMIMO wireless transmissions in the downlink, but the techniques can beapplied in the uplink, in some embodiments.

As discussed above, codebook subset restriction is currently supportedin LTE (Releases 12 and before). With codebook subset restriction, asubset of the precoders in the codebook is restricted so that the UE hasa smaller set of possible precoders to choose from. However, fortwo-dimensional antenna arrays, the codebook size increasessignificantly since the precoders in the codebook need to span twodimensions, typically the horizontal and vertical domain. Signaling acodebook subset restriction (CSR) in LTE prior to Release 13 is by meansof a bitmap with one bit for every precoder in the codebook. Using thesame approach for a two-dimensional codebook can thus impose a largeoverhead. To address the shortcomings of the legacy releases in thecontext of FD-MIMO, it is agreed that LTE Release 13 will support RRCsignaling of Beam-Subset-Restriction bitmap, an i2-Subset-Restrictionbitmap and/or a Rank-Restriction bitmap.

Although the RRC signaling of these bitmaps are agreed, the exactdetails on how these bitmaps should be used to achieve codebook subsetrestriction for LTE Release 13 are still not specified. A problem thatthe present disclosure addresses is how to utilize the agreed bitmaps toachieve codebook subset restriction for Release 13, so as to includeboth two-dimensional beam restriction and rank restriction.

This disclosure provides detailed solutions on how to utilize the agreedbitmaps to achieve codebook subset restriction for Release 13, includingboth two-dimensional beam restriction and rank restriction. Thetechniques disclosed herein comprise the following main components:

-   -   Two different mapping schemes between the bits in        Beam-Subset-Restriction bitmap and the two-dimensional beams are        provided: (1) a second-dimension-first mapping, e.g., a        vertical-dimension-first mapping, and (2) a        first-dimension-first mapping, e.g., a horizontal-first-mapping.    -   Details of how beam restriction across ranks is performed are        presented. In a preferred embodiment, for any rank, a codeword        is not allowed to be reported if the codeword transmits at least        one layer of data on any two-dimensional beam that is not        allowed to be reported (as signaled by the        Beam-Subset-Restriction bitmap).    -   Priority rules are given on the order of applying different        restriction signals when multiple bitmaps (i.e.,        Beam-Subset-Restriction bitmap, i2-Subset-Restriction bitmap,        and/or Rank-Restriction bitmap) are RRC signaled to the UE.

FIG. 6 illustrates a wireless network 100 in which embodiments,disclosed herein, may be carried out. The wireless network 100 includesone or more wireless devices 90, radio network nodes 80, and networknodes, which may include a radio network controller 120, for example.The wireless network may be connected to core network nodes 130. Awireless device 90 may communicate with a radio network node 80 over awireless interface. For example, wireless devices 90 may transmitwireless signals to radio network nodes 80 and/or receive wirelesssignals from radio network nodes 80. The wireless signals may containvoice traffic, data traffic, control signals, and/or any other suitableinformation. The wireless signals may be transmitted over a radio link70.

Radio network nodes 80 may interface with network nodes, such as e.g. aradio network controller 120 in a radio access network 110. A radionetwork controller 120 may control radio network nodes 80 and mayprovide certain radio resource management functions, mobility managementfunctions, and/or other suitable functions. Radio network controller 120may interface with core network node 130. In certain scenarios, radionetwork controller 120 may interface with core network node 130 via aninterconnecting network. Radio network nodes 80 may also interface withcore network node 130. In certain scenarios, radio network node 80 mayinterface with core network node 130 via an interconnecting network.

In some scenarios, core network node 130 may manage the establishment ofcommunication sessions and various other functionalities for wirelessdevices 90. Wireless devices 90 may exchange certain signals with corenetwork node 130 using the non-access stratum (NAS) layer. In non-accessstratum signaling, signals between wireless device 90 and core networknode 130 may be transparently passed through the radio access network.As described with respect to FIG. 6 above, embodiments of network 100may include one or more wireless devices 90, and one or more differenttypes of network nodes capable of communicating (directly or indirectly)with wireless devices 90. Examples of the network nodes include radionetwork nodes 80. The network may also include any additional elementssuitable to support communication between wireless devices 90 or betweena wireless device 90 and another communication device (such as alandline telephone).

Wireless devices 90 and radio network nodes 80 may use any suitableradio access technology, such as long term evolution (LTE),LTE-Advanced, UMTS, High Speed Packet data Access (HSPA), Global Systemfor Mobile Communication (GSM), cdma2000, WiMax, WiFi, another suitableradio access technology, or any suitable combination of one or moreradio access technologies. For purposes of example, various embodimentsmay be described within the context of certain radio accesstechnologies, such as LTE. However, the scope of the disclosure is notlimited to the examples and other embodiments could use different radioaccess technologies. Each of wireless devices 90, radio network nodes80, radio network controller 120, and core network node 130 may includeany suitable combination of hardware and/or software. Examples ofparticular embodiments of wireless devices 90 and radio network nodes 80are described in detail below.

A first aspect of the inventive techniques relates to mapping betweenBeam-Subset-Restriction bits and two-dimensional beams. Let the bitmapfor the Beam-Subset-Restriction parameter be formed by the bit sequencea_(S-1), a_(S-2), . . . a₃, a₂, a₁, a₀, where a₀ is the LeastSignificant Bit (LSB), a_(S-1) is the Most Significant Bit (MSB), andS=N₁O₁N₂O₂. In some embodiments, a bit value of “1” indicates that aparticular two-dimensional) beam is not allowed to be reported in anyrank. In other embodiments, a bit value of “0” indicates that aparticular two-dimensional beam is not allowed to be reported in anyrank.

Let l₁ and l₂ identify a two-dimensional beam that may or may not berestricted, or “forbidden,” where l₁ and l₂ are as defined above.Furthermore, let (l′₁, l′₂) identify a forbidden two-dimensional beam,i.e., a two-dimensional beam that is not allowed to be reported in anyrank, corresponding to a DFT vector with index l′₁ in the firstdimension and a DFT vector with index l′₂ in the second dimension. Theindices l′₁ and l′₂ can be referred to as forbidden dimension indices.If a bit in the Beam-Subset-Restriction bitmap indicates a forbiddentwo-dimensional beam, then this bit corresponds to only one combinationof a forbidden dimension index l′₁ in the first dimension and aforbidden dimension index l′₂ in the second dimension out of theO₁N₁O₂N₂ possible combinations of the first dimension index l₁ and thesecond dimension index l₂.

Note that this technique could be adapted such that the bitmapspecifically identifies two-dimensional beams that should be reported,rather than specifically identifying “forbidden” two-dimensional beams.It will be appreciated that, given a finite set of possibletwo-dimensional beams, specifically identifying allowed two-dimensionalbeams is equivalent to (implicitly) identifying forbiddentwo-dimensional beams. Thus, it will be appreciated that the first andsecond dimension indices l′₁ and l′₂ might, in some embodiments,identify allowed two-dimensional beams, rather than forbidden beams, inwhich case these dimension indices l′₁ and l′₂ are referred to as simplydimension indices, rather than “forbidden” dimension indices.

The mapping between the bits in Beam-Subset-Restriction bitmap and thetwo-dimensional beams can be done in two different ways. In someembodiments, the index n of a bit a_(n) in the bitmap varies most slowlywith the second dimension (e.g., vertical) beam index, and so is labeleda ‘second-dimension-first’ mapping, as shown in FIG. 7. In thesecond-dimension-first mapping scheme, the bit a_(n) can forbid thetwo-dimensional beam with forbidden dimension indices

${l_{1}^{\prime} = {{\left\lfloor \frac{n}{N_{2}O_{2}} \right\rfloor \mspace{14mu} {and}\mspace{14mu} l_{2}^{\prime}} = {n - {N_{2}O_{2}\left\lfloor \frac{n}{N_{2}O_{2}} \right\rfloor}}}},$

where └ ┘ denotes a floor function. Equivalently, n can be calculatedfrom l′₁ and l′₂ with n=l′₂+N₂O₂l′₁. An example of thesecond-dimension-first mapping scheme with (N₁, N₂)=(2,2) and (O₁,O₂)=(4,4) is illustrated in FIG. 8.

In an alternate approach, the index n of a bit a_(n) in the bitmapvaries most slowly with the first dimension (e.g., horizontal) beamindex, and so is labeled a ‘first-dimension-first’ mapping, as shown inFIG. 9. In the first-dimension-first mapping scheme, the bit a_(n) canforbid the two-dimensional beam with forbidden dimension indices

$l_{1}^{\prime} = {{n - {N_{1}O_{1}\left\lfloor \frac{n}{N_{2}O_{2}} \right\rfloor \mspace{14mu} {and}\mspace{14mu} l_{2}^{\prime}}} = {\left\lfloor \frac{n}{N_{2}O_{2}} \right\rfloor.}}$

Equivalently, n can be calculated from l′₁ and l′₂ with n=l′₁+N₁O₁l′₂.An example of the first-dimension-first mapping scheme with (N₁,N₂)=(2,2) and (O₁, O₂)=(4,4) is illustrated in FIG. 10.

Another aspect of the presently disclosed techniques relates to theRank-Restriction parameter. Let the bitmap for the Rank-Restrictionparameter be formed by the bit sequence ã₇, ã₆, . . . ã₃, ã₂, ã₁, ã₀where ã₀ is the LSB and ã₇ is the MSB. The i^(th) bit ã_(i) correspondsto the (i+1)^(th) rank. In some embodiments, a bit value of “1” forã_(i) indicates that codewords corresponding to the (i+1)^(th) rank arenot allowed to be reported. In other embodiments, a bit value of “0” forã_(i) indicates that codewords corresponding to the (i+1)^(th) rank arenot allowed to be reported.

In several embodiments of the presently disclosed techniques andapparatus, the forbidding of a two-dimensional beam depends on the rankand the value of the Config parameter.

Considering the rank 1 Class A codebook of Table 1, a given rank-1codeword W_(m) ₁ _(,m) ₂ _(,n) ⁽¹⁾ as defined in Eq. 4 is forbidden,i.e., not allowed to be reported, if m₁=l′₁ and m₂=l′₂, where (m₁, m₂)are determined by the value of Config (see Table 2) and (l′₁, l′₂)represent the forbidden dimension indices of any two-dimensional beamthat is not allowed to be reported, as signaled by theBeam-Subset-Restriction bitmap.

For the Class A codebooks of ranks 2, 3, and 4 defined above,respectively, a given codeword (which, depending on the rank, can bedefined by Eq. 7, Eq. 8, Eq. 9, or Eq. 10) is forbidden, i.e., notallowed to be reported, if either or both of the following twoconditions are met

m ₁ =l′ ₁ and m ₂ =l′ ₂, simultaneously  Condition 1:

m′ ₁ =l′ ₁ and m′ ₂ =l′ ₂, simultaneously  Condition 2:

where (m₁, m₂) and (m′₁, m′₂) are determined by the value of Config, seeTable 4, Table 6, and Table 8. Furthermore, (l′₁, l′₂) represents anytwo-dimensional beam that is not allowed to be reported, as signaled bythe Beam-Subset-Restriction bitmap.

For the rank 5-8 Class A codebooks described above, a given rank 5-8codeword is forbidden, i.e., not allowed to be reported, if the codewordcontains at least one forbidden two-dimensional beam, as defined jointlyby l′₁ and l′₂. This happens if at least one of the conditions given inTable 13 is met. In Table 13, the δ_(i,j) values are those from the rank5-8 codebooks described above, while i_(1,1) and i_(1,2) are the PMIindices corresponding to the first and second dimensions, as describedabove. The conditions in each column of the table are checked a columnat a time according to the rank (denoted by r). Conditions 1-3 apply tocodewords with ranks 5, 6, 7, or 8, while Condition 4 only applies tocodewords with ranks 7 or 8. For at least one applicable column (i.e.,condition), if forbidden dimension index l′₁ is equal to the cell on thefirst row of the column, and if forbidden dimension index l′₂ issimultaneously equal to the cell on the second row of the column, thencodeword W_(i) _(1,1) _(,i) _(1,2) ^((r)) is forbidden, i.e., notallowed to be reported.

TABLE 13 Rank 5-8 Codeword Restriction Condition 1 Condition 2 Condition3 Condition 4 Rank 5, 6, 7, 8 5, 6, 7, 8 5, 6, 7, 8 7, 8 l′₁ s₁i_(1,1)s₁i_(1,1) + δ_(1,1) s₁i_(1,1) + δ_(1,2) s₁i_(1,1) + δ_(1,3) l′₂s₂i_(1,2) s₂i_(1,2) + δ_(2,1) s₂i_(1,2) + δ_(2,2) s₂i_(1,2) + δ_(2,3)

Embodiments based on Table 13 allow for flexibility, since offset valuesδ_(i,j) are used in the table. Therefore, new codebook configurationscan be specified with different values of δ_(i,j), and this codewordrestriction table can be used without change. However, this approach issomewhat indirect, since δ_(i,j) is used as an intermediate variable. Amore direct approach that avoids the need for δ_(i,j) is shown in Table14 below.

As in Table 13, conditions in Table 14 are grouped according to RI, andthere are 3 sets of conditions for ranks 5, 6, 7, and 8, while there isone condition that applies to only ranks 7 and 8. These conditions areidentified in Table 14. Each condition column is split into two minorcolumns corresponding to the conditions for l′₁ and l′₂. For a given rowwithin a major column, if forbidden dimension index l′₁ is equal to thecell on the left minor column, and if forbidden dimension index l′₂ isequal to the cell on the right minor column, the codeword W_(i) _(1,1)_(,i) _(1,2) ^((r)) is forbidden, i.e., not allowed to be reported. Eachrow of Table 14 corresponds to a codebook configuration of ranks 5-8 anda relationship of the number of ports in the first and second dimension,N₁ and N₂. The codebook configuration and antenna port numberrelationships are shown in the corresponding columns on the left-handside of the table.

TABLE 14 Alternative Rank 5-8 Codeword Restriction Condition 1 Condition2 Condition 3 Condition 4 Codebook Antenna Port 5, 6, 7, 8 5, 6, 7, 8 5,6, 7, 8 7, 8 Configuration Configuration l′₁ l′₂ l′₁ l′₂ l′₁ l′₂ l′₁ l′₂2 N₁ ≥ N₂ or N₁ < s₁i_(1,1) s₂i_(1,2) s₁i_(1,1) + s₂i_(1,2) s₁i_(1,1) +s₂i_(1,2) + s₁i_(1,1) s₂i_(1,2) + N₂ 0₁ 0₁ 0₂ 0₁ 3 N₁ ≥ N₂ s₁i_(1,1)s₂i_(1,2) s₁i_(1,1) + s₂i_(1,2) s₁i_(1,1) + s₂i_(1,2) + s₁i_(1,1) +s₂i_(1,2) + 0₁ 20₁ 0₂ 30₁ 0₂ N₁ < N₂ s₁i_(1,1) s₂i_(1,2) s₁i_(1,1)s₂i_(1,2) + s₁i_(1,1) + s₂i_(1,2) + s₁i_(1,1) + s₂i_(1,2) + 0₂ 0₁ 20₂ 0₁30₂ 4 N₁ ≥ N₂ s₁i_(1,1) s₂i_(1,2) s₁i_(1,1) + s₂i_(1,2) s₁i_(1,1) +s₂i_(1,2) s₁i_(1,1) + s₂i_(1,2) 0₁ 20₁ 30₁ N₁ < N₂ s₁i_(1,1) s₂i_(1,2)s₁i_(1,1) s₂i_(1,2) + s₁i_(1,1) s₂i_(1,2) + s₁i_(1,1) s₂i_(1,2) + 0₂ 20₂30₂

As an alternative or complementary method to identify whether a codewordis forbidden, a two-dimensional beam can be identified as a vector ofcomplex numbers. First we define a forbidden two-dimensional beam vectoras: x=v_(r) ₁ ⊗u_(r) ₂ , where forbidden dimension indices l′₁ and l′₂are determined, as described above, from the index n of bit a_(n) of theBeam-Subset-Restriction parameter. As described in the backgroundsection above, the top N₁N₂ rows of each column i of a given precodingmatrix codeword W^((r)) for r layers can be expressed as atwo-dimensional beamforming vector with the form W^((r))(1:N₁N₂,i)=v_(m)₁ ⊗u_(m) ₂ , where i spans all columns of W^((r)). Then, if each elementof the top N₁N₂ rows of the precoding matrix codeword is the same as theforbidden beam vector x, that two-dimensional beam in that column of theprecoding matrix codeword is the same as the forbidden two-dimensionalbeam. This condition may be expressed for column i as:

W ^((r))(k,i)=x(k) ∀k∈{0,1, . . . ,N ₁ N ₂}.

A precoding matrix codeword from the precoding codebook is not allowedto be reported if the precoding matrix codeword contains at least onecolumn i that is the same as one of the forbidden two-dimensional beams.The check for identifying whether a codeword W^((r)) is forbidden, i.e.,not allowed to be reported, is performed over all forbiddentwo-dimensional beams indicated by forbidden dimension indices (l′₁,l′₂) and all columns (i.e., ∀i) of codeword W^((r)).

In a similar method to identify whether a codeword is forbidden, theforbidden beamforming vector is expressed as a codeword for Config 1 ofa rank-1 FD-MIMO codebook. The Config 1 rank-1 codebook contains alltwo-dimensional beams in the FD-MIMO codebooks for all ranks as itscodewords. Therefore, the two-dimensional beams to be forbidden for anyrank can be identified as codewords in the Config 1 rank-1 codebook. Ifthe bit a_(n) of the Beam-Subset-Restriction parameter indicates thatbeam n is forbidden, forbidden dimension indices l′₁ and l′₂ aredetermined as described above. The corresponding codeword of the Config1 rank-1 codebook is then used to determine if column i of a givenrank-r precoding matrix codeword W^((r)) is forbidden using thefollowing condition:

W ^((r))(k,i)=W _(l) ₁ _(,l) ₂ _(,0) ⁽¹⁾(k) ∀k∈{0,1, . . . ,N ₁ ,N ₂}

Note that W_(l) ₁ _(,l) ₂ _(,0) ⁽¹⁾ is a column vector.

Similarly, for any rank, a codeword from the precoding codebook is notallowed to be reported if the codeword transmits at least one layer ofdata on a two-dimensional beam that is not allowed to be reported, assignaled by the Beam-Subset-Restriction bitmap.

In some alternative embodiments, if a codeword in the codebook for agiven rank, for example as defined in the background section above,contains at least one two-dimensional beam that is not allowed to bereported, as signaled by the Beam-Subset-Restriction bitmap, all thecodewords from the codebook that contains that two-dimensional beam arenot allowed to be reported.

In still other alternative embodiments, which applies when either orboth L′₁>1 and L′₂>1 are satisfied, if at least one two-dimensional beamis not allowed to be reported, as signaled by theBeam-Subset-Restriction bitmap, then all beam groups in any rank,containing this two-dimensional beam are not allowed to be reported.

Another aspect of the presently disclosed techniques and apparatusrelates to codebook subset restriction (CSR) priority rules. When a UEsignaled with more than one of the following codebook subset restrictionbitmaps, different codewords may be forbidden by the different bitmaps.Some rules are needed to specify which restriction bitmap has the higherpriority in case of conflicts, e.g., a codeword is allowed in onerestriction bitmap but not allowed in another restriction bitmap(s).

-   -   The Beam-Subset-Restriction    -   The i2-Subset-Restriction    -   The Rank-Restriction

In some embodiments, a codeword of a particular rank is not allowed inCSI report if it is forbidden by any one of the multiple restrictionbitmaps.

If a UE is RRC configured with the Beam-Subset-Restriction bitmap andthe Rank-Restriction bitmap, but not with the i2-Subset-Restrictionbitmap, the Rank-Restriction bitmap has priority over theBeam-Subset-Restriction bitmap. The forbidden rank(s), i.e., one or morerank(s) that are not allowed to be reported by the UE, are determinedthrough the Rank-Restriction bitmap. The UE applies beam subsetrestriction, as described above, only on codewords associated with ranksthat are not forbidden, (i.e., on codewords associated with ranks thatare allowed to be reported by the UE.

In other embodiments, if a UE is RRC configured with theBeam-Subset-Restriction bitmap and the i2-Subset-Restriction bitmap, butnot with the Rank-Restriction bitmap, then the UE first applies beamsubset restriction, as described above, with higher priority, oncodewords associated with all ranks. Then, additional codewordrestriction is applied through i2-Subset-Restriction, where thei2-Subset-Restriction bitmap may be used to indicate restrictions ofcertain ranks. In some embodiments according to this approach, acodeword for a particular rank is not allowed to be reported by the UEwhen the i2-Subset-Restriction bitmap bits associated with that rankcontains all zeros. Alternatively, a rank may not be allowed to bereported by the UE when the i2-Subset-Restriction bitmap bits associatedwith the rank contains all ones.

In other embodiments, if a UE is RRC configured with theBeam-Subset-Restriction bitmap and the i2-Subset-Restriction bitmap, butnot with the Rank-Restriction bitmap, then the UE first applies thei2-Subset-Restriction, with higher priority, on all codewords per rank,followed by beam subset restriction, as described above, on theremaining codewords associated with each rank.

If the UE is RRC configured with the Beam-Subset-Restriction bitmap, theRank-Restriction bitmap, and the i2-Subset-Restriction bitmap, then theRank-Restriction bitmap is applied first by the UE. Then, the UE appliesbeam subset restriction only on codewords associated with ranks that arenot forbidden. Any additional codeword restrictions are finally realizedthrough applying i2-Subset-Restriction.

In view of the detailed discussion above, it will be appreciated thatseveral embodiments of the presently disclosed techniques correspond toone or more of the following example methods:

-   -   A. A method of restricting which precoding matrix codewords of a        codebook of precoding matrix codewords can be reported in CSI        feedback, comprising providing a bitmap wherein        -   a bit in the bitmap with index n corresponds to only one            combination of a first forbidden dimension index l′₁ and a            second forbidden dimension index l′₂ out of the possible            combinations of the first dimension index l′₁ and the second            dimension index l′₂; and        -   the first forbidden dimension index l′₁ and the second            forbidden dimension index l′₂ identify a two-dimensional            beam, the two-dimensional beam being a vector of complex            numbers comprised within at least one column of a precoding            matrix codeword in the codebook. Here, referring to a            “two-dimensional beam being a vector of complex numbers” is            meant to indicate that the physical two-dimensional beam is            defined by a vector of complex numbers in the codebook.

B. The method of A, where the bits of the bitmap are indexed with indexn, and the index of the bit n in the bitmap is calculated as a linearcombination of the first forbidden dimension index and the secondforbidden dimension index of the form n=l′₁+Cl′₂, where C is a positiveinteger.

C. The method of A, where the bits of the bitmap are indexed with indexn, and the index of the bit n is calculated as a linear combination ofthe first forbidden dimension index and the second forbidden dimensionindex of the form n=l′₂+Cl′₁, where C is a positive integer.

D. The method of any of A-C, further comprising identifying a precodingmatrix codeword as a matrix whose columns are determined using at leastone pair of dimension indices, each pair of dimension indices comprisinga first dimension index and a second dimension index, and for each pairof dimension indices, if the first dimension index is equal to the firstforbidden dimension index l′₁ and the second dimension index is equal tothe second forbidden dimension index l′₂, the precoding matrix codewordis is not allowed to be reported in CSI feedback.

E. The method of A, where for a rank r, any given precoding matrixcodeword of the codebook of precoding matrix codewords is not allowed tobe reported in CSI feedback if transmissions using the given precodingmatrix codeword would have at least one spatially multiplexed layer ofdata on a two-dimensional beam that is not allowed to be reported.

F. The method of A, where for a rank r, any given precoding matrixcodeword of the codebook of precoding matrix codewords is not allowed tobe reported in CSI feedback if at least one column of the givenprecoding matrix codeword has a set of rows that are all equal to thecorresponding elements of any one of the two-dimensional beams that arenot allowed to be reported.

G. A method where the precoding matrix codewords in an entire extendedcodebook table are not allowed to be reported if the extended codebookcontains at least one two-dimensional beam that is not allowed to bereported.

H. A method of applying codebook subset restriction when receivingmultiple configurations, parameters or bitmaps related to codebooksubset restriction, wherein a precoding matrix codeword is forbidden ifthe precoding matrix codeword is forbidden as a result of at least oneof the configurations, parameters or bitmaps.

Embodiments and variations of the above-summarized methods are detailedbelow. It will be appreciated that these methods may be carried out by aradio network node 80 and/or by a wireless device 90, as appropriate.

In the following and according to embodiments herein, then, there areprovided methods performed by/in a radio network node 80 of a wirelessnetwork 100, for configuring a wireless device in a wireless network. Anexample method is shown in FIG. 11 and comprises, as shown at block1110, identifying, among a predetermined codebook of precoding matrixcodewords, a subset of precoding matrix codewords that are not to bereported by the wireless device 90 in channel-state-information (CSI)feedback, i.e., that the wireless device 90 should not report. Note thatwhen referring to the reporting of codewords, the present disclosure mayindicate that the reporting of a codeword is forbidden, is not allowedto be reported, should not be reported, or is not to be reported. Theseare all intended to mean the same thing, in the context of the presentdisclosure.

The method of FIG. 11 further comprises, as shown at block 1120,transmitting, to the wireless device 90, a bitmap identifying the subsetof precoding matrix codewords that are not to be reported by thewireless device 90. Each bit in the bitmap corresponds to only onecombination of a first dimension index l′₁ and a second dimension indexl′₂ out of the possible combinations of the first dimension index l′₁and the second dimension index l′₂, where the forbidden dimension indexl′₁ and the second dimension index l′₂ identify a two-dimensional beam,the two-dimensional beam being defined by a vector of complex numberscomprised within at least one column of a precoding matrix codeword inthe codebook.

In some embodiments, the first dimension index l′₁ and the seconddimension index l′₂ are first and second forbidden dimension indices,respectively, such that the first dimension index l′₁ and the seconddimension index l′₂ identify a forbidden two-dimensional beam for whichcorresponding precoding matrix codewords are not to be reported.

In some embodiments of the method illustrated in FIG. 11, the bits ofthe bitmap are indexed with index n, and the index n for any given bitin the bitmap equals a linear combination of the form n=l′₁+Cl′₂, whereC is a positive integer, and l′₁ and l′₂ are first and second dimensionindices, respectively, for the two-dimensional beam identified by thebit. In other embodiments, the bits of the bitmap are indexed with indexn, and the index n for any given bit in the bitmap equals a linearcombination of the form n=l′₂+Cl′₁, where C is a positive integer, andl′₁ and l′₂ are first and second dimension indices, respectively, forthe two-dimensional beam identified by the bit.

In some embodiments, each precoding matrix codeword is defined as amatrix whose columns are determined using at least one pair of dimensionindices, each pair of dimension indices comprising a first dimensionindex and a second dimension index. In these embodiments, each bit of apredetermined value in the bitmap indicates one or more precoding matrixcodewords where, for each precoding matrix codeword, the precodingmatrix codeword is not allowed to be reported in CSI feedback if, for atleast one pair of dimension indices for the precoding matrix codeword,the first dimension index is equal to the first dimension index l′₁ andthe second dimension index is equal to the second dimension index l′₂.

In some embodiments, each bit of a predetermined value in the bitmapindicates that, for a rank r, any given precoding matrix codeword of thecodebook of precoding matrix codewords is not allowed to be reported inCSI feedback if transmissions using the precoding matrix codeword wouldhave at least one spatially multiplexed layer of data on atwo-dimensional beam identified by the bit. In some embodiments, eachbit of a predetermined value in the bitmap indicates that, for a rank r,a precoding matrix codeword of the codebook of precoding matrixcodewords is not allowed to be reported in CSI feedback if at least onecolumn of the precoding matrix codeword has a set of rows that are allequal to the corresponding elements of the two-dimensional beamidentified by the bit.

In some embodiments or instances of the method shown in FIG. 11, theradio network node 80 subsequently receives, from the wireless device90, CSI feedback reporting a precoding matrix codeword that is not amongthe identified subset of precoding matrix codewords that are not to bereported by the wireless device 90 in CSI feedback. This is shown atblock 1130. The radio network node 80 then applies the reportedprecoding matrix codeword to one or more two-dimensional multiple-inputmultiple-output transmissions to the wireless device 90, as shown atblock 1140.

According to embodiments herein, there is further provided a radionetwork node 80 for configuring a wireless device in a wireless network100, the radio network node 80 comprising processing circuitry and amemory, the memory containing instructions executable by the processingcircuitry, whereby the radio network node 80 is adapted and/orconfigured and/or operative to identify, among a predetermined codebookof precoding matrix codewords, a subset of precoding matrix codewordsthat are not to be reported by the wireless device 90 inchannel-state-information (CSI) feedback, and to transmit, to thewireless device 90, a bitmap identifying the subset of precoding matrixcodewords that are not to be reported by the wireless device 90. Again,each bit in the bitmap corresponds to only one combination of a firstdimension index l′₁ and a second dimension index l′₂ out of the possiblecombinations of the first dimension index l′₁ and the second dimensionindex l′₂, where the first dimension index l′₁ and the second dimensionindex l′₂ identify a two-dimensional beam, the two-dimensional beambeing defined a vector of complex numbers comprised within at least onecolumn of a precoding matrix codeword in the codebook.

Again, in some embodiments, the first dimension index l′₁ and the seconddimension index l′₂ are first and second forbidden dimension indices,respectively, such that the first dimension index l′₁ and the seconddimension index l′₂ identify a forbidden two-dimensional beam for whichcorresponding precoding matrix codewords are not to be reported.

Details regarding further features of the corresponding methodembodiments have already been provided above so it is consideredunnecessary to repeat such details. This goes for all embodimentsrelated to the radio network node 80 that will be disclosed below.

In the following and according to embodiments herein, there are providedmethods, by/in a wireless device 90 operating in a wireless network 100.An example method is illustrated in FIG. 12 and comprises, as shown atblock 1210, receiving, from a radio network node 80, a bitmapindicating, among a predetermined codebook of precoding matrixcodewords, a subset of precoding matrix codewords that are not to bereported by the wireless device 90 in channel-state-information (CSI)feedback. The method further comprises, as shown at block 1220,identifying, using the bitmap, the subset of precoding matrix codewordsthat are not to be reported by the wireless device 90 in CSI feedback.Each bit in the bitmap corresponds to only one combination of a firstdimension index l′₁ and a second dimension index l′₂ out of the possiblecombinations of the first dimension index l′₁ and the second dimensionindex l′₂, where the first dimension index l′₁ and the second dimensionindex l′₂ identify a two-dimensional beam, the two-dimensional beambeing defined by a vector of complex numbers comprised within at leastone column of a precoding matrix codeword in the codebook. As above, insome embodiments, the first dimension index l′₁ and the second dimensionindex l′₂ are first and second forbidden dimension indices,respectively, such that the first dimension index l′₁ and the seconddimension index l′₂ identify a forbidden two-dimensional beam for whichcorresponding precoding matrix codewords are not to be reported.

In some embodiments of the method illustrated in FIG. 12, the bits ofthe bitmap are indexed with index n, and the index n for any given bitin the bitmap equals a linear combination of the form n=l′₁+Cl′₂, whereC is a positive integer, and l′₁ and l′₂ are first and second dimensionindices, respectively, for the two-dimensional beam identified by thebit. In other embodiments, the bits of the bitmap are indexed with indexn, and the index n for any given bit in the bitmap equals a linearcombination of the form n=l′₂+Cl′₁, where C is a positive integer, andl′₁ and l′₂ are first and second dimension indices, respectively, forthe two-dimensional beam identified by the bit.

In some embodiments, each precoding matrix codeword is defined as amatrix whose columns are determined using at least one pair of dimensionindices, each pair of dimension indices comprising a first dimensionindex and a second dimension index. In these embodiments, each bit of apredetermined value in the bitmap indicates one or more precoding matrixcodewords where, for each precoding matrix codeword, the precodingmatrix codeword is not allowed to be reported in CSI feedback if, for atleast one pair of dimension indices for the precoding matrix codeword,the first dimension index is equal to the first dimension index l′₁ andthe second dimension index is equal to the second dimension index l′₂.

In some embodiments, each bit of a predetermined value in the bitmapindicates that, for a rank r, any given precoding matrix codeword of thecodebook of precoding matrix codewords is not allowed to be reported inCSI feedback if transmissions using the precoding matrix codeword wouldhave at least one spatially multiplexed layer of data on atwo-dimensional beam identified by the bit. In some embodiments, eachbit of a predetermined value in the bitmap indicates that, for a rank r,a precoding matrix codeword of the codebook of precoding matrixcodewords is not allowed to be reported in CSI feedback if at least onecolumn of the precoding matrix codeword has a set of rows that are allequal to the corresponding elements of the two-dimensional beamidentified by the bit.

In some embodiments or instances of the method shown in FIG. 12, thewireless device 90 subsequently selects a precoding matrix codeword,from precoding matrix codewords in the predetermined codebook other thanthose precoding matrix codewords in the identified subset. Thisselecting, which is shown at block 1230 of FIG. 12, is based on one ormore channel measurements. The method may further comprises, as shown atblock 1240, transmitting, to the radio network node 80, CSI feedbackreporting the selected precoding matrix codeword.

According to embodiments herein, there is further provided a wirelessdevice 90, comprising a processing circuitry and a memory, the memorycontaining instructions executable by the processing circuitry, wherebythe wireless device 90 is adapted and/or configured and/or operative toreceive, from a radio network node 80, a bitmap indicating, among apredetermined codebook of precoding matrix codewords, a subset ofprecoding matrix codewords that are not to be reported by the wirelessdevice 90 in channel-state-information (CSI) feedback; and to identify,using the bitmap, the subset of precoding matrix codewords that are notto be reported by the wireless device 90 in CSI feedback. Each bit inthe bitmap corresponds to only one combination of a first dimensionindex l′₁ and a second dimension index l′₂ out of the possiblecombinations of the first dimension index l′₁ and the second dimensionindex l′₂, and wherein the first dimension index l′₁ and the seconddimension index l′₂ identify a two-dimensional beam, the two-dimensionalbeam being defined by a vector of complex numbers comprised within atleast one column of a precoding matrix codeword in the codebook. Detailsregarding features of the corresponding method embodiment have alreadybeen provided above so it is considered unnecessary to repeat suchdetails. This goes for all embodiments related to the wireless device 90that will be disclosed below.

Referring to FIG. 13 there is illustrated a block diagram of exemplarycomponents of a radio network node 80 in accordance with embodimentsdisclosed above. The radio network node 80 may comprise a radiotransceiver 1320, which in turn includes a receiver circuit and atransmitter circuit, which are coupled, in some embodiments, to atwo-dimensional array of antennas (not shown). Radio network nodefurther comprises a processing circuit 1310, which in turn comprises oneor more processors, e.g., microprocessors, microcontrollers, digitalsignal processors, and the like, a memory circuit 1314. Memory circuit1314, which may comprise one or several types of memory, such as Flash,RAM, ROM, etc., stores program code 1316 for execution by processor(s)1312; the program code 1316 includes instructions for controlling theoperation of radio transceiver 1320 and for carrying out a method likethose described above in connection with FIG. 11, for example. Memorycircuit 1314 further provides storage for program data 1318, which maybe generated and/or utilized by the executing program code 1316 in thecourse of carrying out one or more of the methods described herein.Processing circuit 1310, which may be implemented as one or moreapplication-specific integrated circuits (ASICs) in some embodiments,may further include additional digital logic configured to carry out oneor more of the operations described herein, alone, or in conjunctionwith processor(s) 1312, and may further include additional supportingcircuitry, e.g., for regulating power supplies, generating necessaryclock or other timing signals, converting analog signals to digitalsignals and/or vice-versa, etc.

The memory 1314 may contain instructions executable by the processor(s)1310 whereby the radio network node 80 is operative to perform methodsteps described herein as implemented in a radio network node. There isalso provided a computer program comprising computer readable code meanswhich, when run in the radio network node 80, e.g., by means of theprocessor or processing circuit 1310, causes the radio network node 80to perform the above described method steps, which include, in someembodiments, identifying, among a predetermined codebook of precodingmatrix codewords, a subset of precoding matrix codewords that are not tobe reported by the wireless device 90 in CSI feedback, and transmitting,to the wireless device 90, a bitmap identifying the subset of precodingmatrix codewords that are not to be reported by the wireless device 90.

It will be appreciated that all or parts of radio network node 80 mayalso be conceived as comprising one or more functional modules, witheach functional module being implemented with hardware and/or withhardware configured with appropriate software or firmware, andcorresponding to one or more of the method steps described herein asimplemented in a radio network node 80. Thus, for example, radio networknode 80 may be understood as comprising an identification module foridentifying, among a predetermined codebook of precoding matrixcodewords, a subset of precoding matrix codewords that are not to bereported by the wireless device 90 in CSI feedback, and as furthercomprising a transmitter module for transmitting, to the wireless device90, a bitmap identifying the subset of precoding matrix codewords thatare not to be reported by the wireless device 90. In some embodiments,radio network node 80 may be understood to further comprise a receivermodule for receiving, from the wireless device 90, CSI feedbackreporting a precoding matrix codeword that is not among the identifiedsubset of precoding matrix codewords that are not to be reported by thewireless device 90 in CSI feedback, as well as a precoder module forapplying the reported precoding matrix codeword to one or moretwo-dimensional multiple-input multiple-output transmissions to thewireless device.

Referring to FIG. 14 there is illustrated a block diagram of exemplarycomponents of a wireless device 90 in accordance with embodimentsdisclosed above. The wireless device 90 may comprise a radio transceiver1420, which in turn includes a receiver circuit and a transmittercircuit, which are coupled, in some embodiments, to a two-dimensionalarray of antennas (not shown). Radio network node further comprises aprocessing circuit 1410, which in turn comprises one or more processors,e.g., microprocessors, microcontrollers, digital signal processors, andthe like, a memory circuit 1414. Memory circuit 1414, which may compriseone or several types of memory, such as Flash, RAM, ROM, etc., storesprogram code 1416 for execution by processor(s) 1412; the program code1416 includes instructions for controlling the operation of radiotransceiver 1420 and for carrying out a method like those describedabove in connection with FIG. 12, for example. Memory circuit 1414further provides storage for program data 1418, which may be generatedand/or utilized by the executing program code 1416 in the course ofcarrying out one or more of the methods described herein. Processingcircuit 1410, which may be implemented as one or moreapplication-specific integrated circuits (ASICs) in some embodiments,may further include additional digital logic configured to carry out oneor more of the operations described herein, alone, or in conjunctionwith processor(s) 1412, and may further include additional supportingcircuitry, e.g., for regulating power supplies, generating necessaryclock or other timing signals, converting analog signals to digitalsignals and/or vice-versa, etc.

The memory 1414 may contain instructions executable by the processor(s)or processing circuit 1410 whereby the wireless device 90 is operativeto perform the previously described method steps. There is also provideda computer program comprising computer readable code means which whenrun in the wireless device 90, e.g., by means of the processor orprocessing circuit 1410, causes the wireless device 90 to perform theabove described method steps, which include, in some embodiments,receiving, from a radio network node 80, a bitmap indicating, among apredetermined codebook of precoding matrix codewords, a subset ofprecoding matrix codewords that are not to be reported by the wirelessdevice 90 in CSI feedback, and identifying, using the bitmap, the subsetof precoding matrix codewords that are not to be reported by thewireless device 90 in CSI feedback.

It will be appreciated that all or parts of wireless device 90 may alsobe conceived as comprising one or more functional modules, with eachfunctional module being implemented with hardware and/or with hardwareconfigured with appropriate software or firmware, and corresponding toone or more of the method steps described herein as implemented in awireless device 90. Thus, for example, wireless device 90 may beunderstood as comprising a receiver module for receiving, from a radionetwork node 80, a bitmap indicating, among a predetermined codebook ofprecoding matrix codewords, a subset of precoding matrix codewords thatare not to be reported by the wireless device 90 in CSI feedback, aswell as an identification module for identifying, using the bitmap, thesubset of precoding matrix codewords that are not to be reported by thewireless device 90 in CSI feedback. In some embodiments, wireless devicemay be understood to further comprise a selection module for selecting aprecoding matrix codeword from precoding matrix codewords in thepredetermined codebook other than those precoding matrix codewords inthe identified subset, where said selecting is based on one or morechannel measurements, as well as a transmitter module for transmitting,to the network node 80, CSI feedback reporting the selected precodingmatrix codeword.

A wireless network 100 may be any communication system as defined by3GPP, such as UMTS, LTE, GSM, CDMA2000 or a core network such as EPS orany combination of those.

Throughout this disclosure, the word “comprise” or “comprising” has beenused in a non-limiting sense, i.e. meaning “consist at least of”.Although specific terms may be employed herein, they are used in ageneric and descriptive sense only and not for purposes of limitation.In particular, it should be noted that although terminology from 3GPPand IEEE802.11EEE has been used in this disclosure to exemplify theinvention, this should not be seen as limiting the scope of theinvention to only the aforementioned system. Other communicationsystems, including LTE or LTE-A (LTE-Advanced) and WiMax may alsobenefit from exploiting the ideas covered within this disclosure.

Notably, modifications and other embodiments of the disclosedinvention(s) will come to mind to one skilled in the art having thebenefit of the teachings presented in the foregoing descriptions and theassociated drawings. Therefore, it is to be understood that theinvention(s) is/are not to be limited to the specific embodimentsdisclosed and that modifications and other embodiments are intended tobe included within the scope of this disclosure. Although specific termsmay be employed herein, they are used in a generic and descriptive senseonly and not for purposes of limitation.

1-32. (canceled)
 33. A method, in a radio network node, for configuringa wireless device in a wireless network, the method comprising:identifying, among a predetermined codebook of precoding matrixcodewords, a subset of precoding matrix codewords that are not to bereported by the wireless device in channel-state-information (CSI)feedback; and transmitting, to the wireless device, a bitmap identifyingthe subset of precoding matrix codewords that are not to be reported bythe wireless device; wherein each bit in the bitmap corresponds to onlyone combination of a first dimension index l′₁ and a second dimensionindex l′₂ out of the possible combinations of the first dimension indexl′₁ and the second dimension index l′₂, and wherein the first dimensionindex l′₁ and the second dimension index l′₂ identify a two-dimensionalbeam, the two-dimensional beam being defined by a vector of complexnumbers comprised within at least one column of a precoding matrixcodeword in the codebook.
 34. The method of claim 33, wherein the firstdimension index l′₁ and the second dimension index l′₂ are first andsecond forbidden dimension indices, respectively, such that the firstdimension index l′₁ and the second dimension index l′₂ identify aforbidden two-dimensional beam for which corresponding precoding matrixcodewords are not to be reported.
 35. The method of claim 33, whereinthe bits of the bitmap are indexed with index n and the index n for anygiven bit in the bitmap equals a linear combination of the formn=l′₁+Cl′₂, where C is a positive integer, and l′₁ and l′₂ are first andsecond dimension indices, respectively, for the two-dimensional beamidentified by the bit.
 36. The method of claim 33, wherein the bits ofthe bitmap are indexed with index n and the index n for any given bit inthe bitmap equals a linear combination of the form n=l′₂+Cl′₁, where Cis a positive integer, and l′₁ and l′₂ are first and second dimensionindices, respectively, for the two-dimensional beam identified by thebit.
 37. The method of claim 33, wherein each precoding matrix codewordis defined as a matrix whose columns are determined using at least onepair of dimension indices, each pair of dimension indices comprising afirst dimension index and a second dimension index, and wherein each bitof a predetermined value in the bitmap indicates one or more precodingmatrix codewords where, for each precoding matrix codeword, theprecoding matrix codeword is not allowed to be reported in CSI feedbackif, for at least one pair of dimension indices for the precoding matrixcodeword, the first dimension index is equal to the first dimensionindex l′₁ and the second dimension index is equal to the seconddimension index l′₂.
 38. The method of claim 33, wherein each bit of apredetermined value in the bitmap indicates that, for a rank r, anygiven precoding matrix codeword of the codebook of precoding matrixcodewords is not allowed to be reported in CSI feedback if transmissionsusing the precoding matrix codeword would have at least one spatiallymultiplexed layer of data on a two-dimensional beam identified by thebit.
 39. The method of claim 33, wherein each bit of a predeterminedvalue in the bitmap indicates that, for a rank r, a precoding matrixcodeword of the codebook of precoding matrix codewords is not allowed tobe reported in CSI feedback if at least one column of the precodingmatrix codeword has a set of rows that are all equal to thecorresponding elements of the two-dimensional beam identified by thebit.
 40. The method of claim 33, further comprising: receiving, from thewireless device, CSI feedback reporting a precoding matrix codeword thatis not among the identified subset of precoding matrix codewords thatare not to be reported by the wireless device in CSI feedback; andapplying the reported precoding matrix codeword to one or moretwo-dimensional multiple-input multiple-output transmissions to thewireless device.
 41. A method, in a wireless device operating in awireless network, the method comprising: receiving, from a radio networknode, a bitmap indicating, among a predetermined codebook of precodingmatrix codewords, a subset of precoding matrix codewords that are not tobe reported by the wireless device in channel-state-information (CSI)feedback; and identifying, using the bitmap, the subset of precodingmatrix codewords that are not to be reported by the wireless device inCSI feedback, wherein each bit in the bitmap corresponds to only onecombination of a first dimension index l′₁ and a second dimension indexl′₂ out of the possible combinations of the first dimension index l′₁and the second dimension index l′₂, and wherein the first dimensionindex l′₁ and the second dimension index l′₂ identify a two-dimensionalbeam, the two-dimensional beam being defined by a vector of complexnumbers comprised within at least one column of a precoding matrixcodeword in the codebook.
 42. The method of claim 41, wherein the firstdimension index l′₁ and the second dimension index l′₂ are first andsecond forbidden dimension indices, respectively, such that the firstdimension index l′₁ and the second dimension index l′₂ identify aforbidden two-dimensional beam for which corresponding precoding matrixcodewords are not to be reported.
 43. The method of claim 41, whereinthe bits of the bitmap are indexed with index n and the index n for anygiven bit in the bitmap equals a linear combination of the formn=l′₁+Cl′₂, where C is a positive integer, and l′₁ and l′₂ are first andsecond dimension indices, respectively, for the two-dimensional beamidentified by the bit.
 44. The method of claim 41, wherein the bits ofthe bitmap are indexed with index n and the index n for any given bit inthe bitmap equals a linear combination of the form n=l′₂+Cl′₁, where Cis a positive integer, and l′₁ and l′₂ are first and second dimensionindices, respectively, for the two-dimensional beam identified by thebit.
 45. The method of claim 41, wherein each precoding matrix codewordis defined as a matrix whose columns are determined using at least onepair of dimension indices, each pair of dimension indices comprising afirst dimension index and a second dimension index, and wherein each bitof a predetermined value in the bitmap indicates one or more precodingmatrix codewords where, for each precoding matrix codeword, theprecoding matrix codeword is not allowed to be reported in CSI feedbackif, for at least one pair of dimension indices for the precoding matrixcodeword, the first dimension index is equal to the first dimensionindex l′₁ and the second dimension index is equal to the seconddimension index l′₂.
 46. The method of claim 41, wherein each bit of apredetermined value in the bitmap indicates that, for a rank r, anygiven precoding matrix codeword of the codebook of precoding matrixcodewords is not allowed to be reported in CSI feedback if transmissionsusing the precoding matrix codeword would have at least one spatiallymultiplexed layer of data on a two-dimensional beam identified by thebit.
 47. The method of claim 41, wherein each bit of a predeterminedvalue in the bitmap indicates that, for a rank r, a precoding matrixcodeword of the codebook of precoding matrix codewords is not allowed tobe reported in CSI feedback if at least one column of the precodingmatrix codeword has a set of rows that are all equal to thecorresponding elements of the two-dimensional beam identified by thebit.
 48. The method of claim 41, further comprising: selecting aprecoding matrix codeword, from precoding matrix codewords in thepredetermined codebook other than those precoding matrix codewords inthe identified subset, wherein said selecting is based on one or morechannel measurements; and transmitting, to the network node, CSIfeedback reporting the selected precoding matrix codeword.
 49. A radionetwork node, for configuring a wireless device in a wireless network,the radio network node comprising processing circuitry and a memory,said memory containing instructions executable by said processingcircuitry, whereby said radio network node is configured to: identify,among a predetermined codebook of precoding matrix codewords, a subsetof precoding matrix codewords that are not to be reported by thewireless device in channel-state-information (CSI) feedback; andtransmit, to the wireless device, a bitmap identifying the subset ofprecoding matrix codewords that are not to be reported by the wirelessdevice; wherein each bit in the bitmap corresponds to only onecombination of a first dimension index l′₁ and a second dimension indexl′₂ out of the possible combinations of the first dimension index l′₁and the second dimension index l′₂, and wherein the first dimensionindex l′₁ and the second dimension index l′₂ identify a two-dimensionalbeam, the two-dimensional beam being defined by a vector of complexnumbers comprised within at least one column of a precoding matrixcodeword in the codebook.
 50. The radio network node of claim 49,wherein the first dimension index l′₁ and the second dimension index l′₂are first and second forbidden dimension indices, respectively, suchthat the first dimension index l′₁ and the second dimension index l′₂identify a forbidden two-dimensional beam for which correspondingprecoding matrix codewords are not to be reported.
 51. The radio networknode of claim 49, wherein the memory containing instructions executableby said processing circuitry further comprises instructions forreceiving, from the wireless device, CSI feedback reporting a precodingmatrix codeword that is not among the identified subset of precodingmatrix codewords that are not to be reported by the wireless device inCSI feedback, and applying the reported precoding matrix codeword to oneor more two-dimensional multiple-input multiple-output transmissions tothe wireless device.
 52. A wireless device for operating in a wirelessnetwork, the wireless device comprising processing circuitry and amemory, said memory containing instructions executable by saidprocessing circuitry, whereby said wireless device is configured to:receive, from a radio network node, a bitmap indicating, among apredetermined codebook of precoding matrix codewords, a subset ofprecoding matrix codewords that are not to be reported by the wirelessdevice in channel-state-information (CSI) feedback; and identify, usingthe bitmap, the subset of precoding matrix codewords that are not to bereported by the wireless device in CSI feedback, wherein each bit in thebitmap corresponds to only one combination of a first dimension indexl′₁ and a second dimension index l′₂ out of the possible combinations ofthe first dimension index l′₁ and the second dimension index l′₂, andwherein the first dimension index l′₁ and the second dimension index l′₂identify a two-dimensional beam, the two-dimensional beam being definedby a vector of complex numbers comprised within at least one column of aprecoding matrix codeword in the codebook.
 53. The wireless device ofclaim 52, wherein the first dimension index l′₁ and the second dimensionindex l′₂ are first and second forbidden dimension indices,respectively, such that the first dimension index l′₁ and the seconddimension index l′₂ identify a forbidden two-dimensional beam for whichcorresponding precoding matrix codewords are not to be reported.
 54. Thewireless device of claim 52, wherein the memory containing instructionsexecutable by said processing circuitry further comprises instructionsfor selecting a precoding matrix codeword, from precoding matrixcodewords in the predetermined codebook other than those precodingmatrix codewords in the identified subset, wherein said selecting isbased on one or more channel measurements, and transmitting, to thenetwork node, CSI feedback reporting the selected precoding matrixcodeword.